Dialog During Gameplay

For the longest time, video games told stories only through dialog that would occur either during cutscenes, or when you walked up to a person and hit the button to talk to them.

But now, with the growing trend toward more cinematic and story-oriented games, companies are starting to have their characters talk and hold conversations during gameplay.

Naturally, this occurs in games where a group of characters travel together, since otherwise, there'd be no-one for the hero to talk to (though many games did have solo heroes making one-liners—or just chatting with themselves). Oftentimes, the heroes will be traveling the countryside, wandering through a town, or so on, and the characters will talk to each other. Or they might remark on something they just saw, or something that recently happened.

This tends to make the characters feel more "alive" by showing their personality, but it also has the benefit of conveying story and character without hurting the flow of gameplay. If Nathan Drake quips with Elena and Chloe while you're making him explore a ruined city, then you don't have to stop what you're doing just to watch the characters talk. Plus, it gives more of a feel of actually being there with those characters, to hear them conversing while you're controlling the lead hero.

On the other hand, this kind of dialog is easy to miss while concentrating on the game, especially if there are no subtitles and there is action going on. So it's best limited to background detail, with actual game-critical information given in cutscenes.

On the technical side, including unobtrusive dialogue is handy to fill in the boring sequences of trekking across safe/already explored locations. For the same reason, it is sometimes used in conjunction with Dynamic Loading.

Note: If the gameplay stops for any reason for the characters to talk, that's not this trope. Therefore, the skits from the Namco Tales series don't count. Also, if it doesn't involve characters talking to each other and only involves the main character remarking on things out loud, it's not dialog.

See also Boss Banter, which is when bosses taunt the player during gameplay - not quite dialog (as there's no back-and-forth).

Examples of Dialog During Gameplay include:

The Uncharted series lives and breathes this trope. There's a lot of conversations the characters have with each other during gameplay, not just during exploration but also sometimes even during battle!
BioWare's RPGs frequently have this, as part of the company's traditional attention to characters. The fandom's term for this is "Party Banter", since most of the dialogue takes place between active party members.
- The Baldurs Gate series started the tradition but there, the party members with opposing world views would start arguments and draw on the PC for arbitration, thus making it a regular cutscene. Sometimes, however, they would spontaneously compliment each other while traveling, playing this straight.
- The Mass Effect series follows suit, with squad members conversing behind Shepard's back, especially during the elevator rides used to conceal level loading in the first game.
- The Dragon Age series has a set of predetermined locations, passing through which would trigger dialogue between two (sometimes all three) NPCs accompanying the player. Each pair of characters has 5-6 dialogue bits that play out sequentially, regardless in what order you visit the trigger locations (though some play only after certain plot events), and each bit reveals hidden aspects of their personalities (like Leliana catching Sten playing with a kitten, or Zevran hitting on Morrigan). Dragon Age II even lets the Suddenly Voiced Player Character participate in the banter.
Sonic and The Secret Rings has Sonic the Hedgehog accompanied by a fairy/light that follows him around, and sometimes the two talk to each other.
- The same happens in Sonic Heroes, where the team members talk among themselves during gameplay.
Several of the Spider-Man video games have Spiderman and the bad guys toss back and forth verbal barbs at each other. Sometimes townspeople will talk to Spidey or shout up at him while he's swinging around the city, and he'll talk back.
In Batman: Arkham Asylum, Batman will converse with Oracle to discuss objectives and such during gameplay.
In the Ace Combat series, most of the dialogue takes place while you are flying/dogfighting, though the really important (story-relevant or character-building) exchanges take place during the quiet getting-to-the-target-airspace sequences. In Ace Combat 5 The Unsung War, you could even participate in it with simple yes/no answers (if you didn't press a corresponding button due to being too busy actually playing, the prompt disappeared after a few seconds and the dialogue continued).
Rogue Galaxy had a feature called "Active Chat" (a possible title) where as you run about each planet, the active members in your team quip random comments. Many of these were context-sensitive, reflecting on the current situation/objective, the previous Random Encounter, the surrounding environment, how long the player has been running around (or standing still), how long it's been since they used a Save Point, or so on.
Final Fantasy XIII has this; when you're walking around, sometimes your party members will comment on stuff like the scenery in the corner of the screen.
This was an innovation in Metal Gear Solid 4: Guns of the Patriots; previously, whenever Otacon or your other Voice with an Internet Connection wanted to talk to you, they'd have to interrupt the gameplay by pulling up the Codec menu to talk to you. In MGS4, Otacon gives tips to you right in the middle of gameplay; this becomes vital if, for example, you get totally lost inside a collapsed building.
Neopets browser RPG Neo Quest II has a few lines the characters can randomly utter during any move outside fights. Each character has their own lines.
Oblivion has NPCs getting into conversations about rumors and current events with each other, while the player is walking around.
Harry Potter and the Order of the Phoenix has Ron and Hermione talking in the background about plot related subjects at regular intervals while you walk from place to place.
In Deadly Premonition, when you have passengers in your car, there's conversation between York and his passengers. York can also have one-way conversations with his invisible friend Zach when he's driving solo.
The Left 4 Dead series has lots of this. Characters talk to each other frequently, mostly yelling out information (such as enemy positions), but sometimes hold brief conversations as well.
This goes all the way back to Space Ace, with Dexter and Kimberly exchanging witty banter (and exposition) during action scenes.
Tales of Symphonia: Dawn of the New World had conversations mid-battle, usually as the result of player action (i.e. using items, taking a lot of damage).

Marta: You're using too many Artes!
Emil: It's to win!

- This has become very common amongst many games in the Tales Of series. Frequently, the beginning of a Boss Battle will have dialogue between the participants during the fight itself. Party members may comment on the player's tactics, such as using the same technique repeatedly or running around the enemies and not attacking.
In Famous has conversations with your companions when you're on an escort mission sometimes, and you regularly have Cole talking to various people on the phone during gameplay. One time Cole's jerk friend Zeke calls up in the middle of a battle, and won't take the hint that now is not the time to be talking about cool names for Cole's new superpowers.
Assassin's Creed occasionally has the voices of your support team appearing during gameplay, and regularly has dialogue during escort missions. Boss fights sometimes have the player character and the boss trading words.
Beyond Good and Evil has protagonist Jade and her partner characters talking constantly with her. Some of it allows them to exercise their Exposition Fairy sides, but some of it is simply for flavor or character-building.
There's lots of chatter with your wingmen in the Star Fox series. Sometimes enemies exchange taunts with the heroes, and sometimes other characters talk to the Star Fox team. This has been happening since the first game, which originally used only text and no voice acting to convey the dialog.
Kid Icarus: Uprising has a lot of this during both gameplay types - the flying and the on-ground fighting. Pit has a lot of back-and-forth dialog with Palutena, and other characters, such as bosses, have a lot to say during gameplay as well. Some of it is story-related, while a lot of it is comedic banter.
Grand Theft Auto: San Andreas has this during some boss scenes. Thus, sometimes delaying the death blow so the player can hear what else the opponent has to say.
- Grand Theft Auto IV has the above, with the addition of conversations that take place while you are driving to missions. Almost every mission has a conversation, and there are even alternate conversations that occur if you have failed the mission and are attempting it for the second time.
In Scarface the World Is Yours, in the 'storage area' an extra summoned mook will sometimes decide to get into a verbal shouting match with the mook that shows up because it's a storage area.
Used in Meta Knight's Revenge in Kirby Super Star. The villainous crew constantly banter among each other (even giving out gameplay/boss hints) while you play through the game.
Fossil Fighters includes Combat Commentators discussing the battles going on, via text boxes on the DS's top screen. Like with Kirby Super Star, you can pick up tips if you pay attention.
All conversations in Dead Space and Dead Space 2 happen in real time through the videologs projected from Isaac´s RIG
Happens while the player is platforming in Prince of Persia: Sands of Time trilogy. Sometimes, the conversation is distracting and leads to the player´s death, making them miss out the rest of the conversation.
- Likewise, there is a lot of banter between Prince and Elika in the 2008 version.
L.A. Noire likes to include dialogue while you are driving to somewhere.
Ditto Mafia: The City of Lost Heaven.
All the dialogue between Faith and Merc in Mirror's Edge happens via Faith's headset while she is running really fast. Apparently, she is just that good at keeping her breath steady.
Almost all of the storytelling in Sonny is done via this, since the game is essentially a long string of battles with only a single fairly short cutscene in between each chapter.
Silent Hill: Shattered Memories allows Harry and anyone currently travelling with him to hold a conversation en route to their destination, either on foot or in a vehicle.
The upcoming Naughty Dog title The Last of Us has not only story-related dialog, but also banter that occurs before, during and after fights. Even when a fight is not finished, Ellie might exclaim "Holy shit, Joel!" when Joel lights someone on fire with a molotov cocktail, and Joel will tell her not to freak.