Lockdown

Exactly What It Says on the Tin. A location is isolated by means of locking every door/window/refrigerator/air vent/other entrance in the area so that no one can get in or out of the building. For the medical cases surrounding this, it is a quarantine. Armed guards may also be posted, depending on whether or not the military is involved. Has nothing to do with a Cybertronian bounty hunter.

When this begins, the odds are 99% someone will attempt a Indy Hat Roll.

Also see: Trapped in Containment. Quite likely to result in Failsafe Failure or Didn't See That Coming if the plot demands whatever is in lockdown escapes.

Examples of Lockdown include:

Anime & Manga

Mahou Sensei Negima has a set of Lockdown doors in Library Island, which Yue triggers upon having a Heroic BSOD when she discovers herself in a Love Triangle involving her best friend and her teacher.
An early episode of Keroro Gunsou features the Hinata house going into Lockdown...because Keroro has a cavity. A cavity caused by tiny aliens, but still...
In Irresponsible Captain Tylor, after Tylor is kidnapped the command takes the opportunity to put the whole crew in quarantine because (they claim) of the alien virus the crew were infected with to force him to surrender.

Film

[[Quarantine (film)|Quarantine] (2008).
The Andromeda Strain (without human input).
The first Resident Evil film (without human input).
Star Wars:
- "Close the blast doors!"
- "Open the blast doors, open the blast doors!"
WarGames
During the film Men in Black II, the MIB HQ goes into Code 101 Lockdown.
X-Men Origins: Wolverine when Wolverine is escaping the Weapon X facility.
Total Recall. Happens twice. Once when Quaid arrives on Mars and later when Cohaagen locks down a sector which has disobeyed him:

Technician: Sir, the oxygen level is bottoming out in Sector G. What do you want me to do about it?
Vilos Cohaagen: [as if obvious] Don't do anything.
Technician: But they won't last an hour, sir.
Vilos Cohaagen: Fuck 'em. It'll be a good lesson to the others.

Warning Sign has a full quarantine lockdown in the Biotek facility. And apparently their employees are idiots, because they stare at the closing shutters and alarms in confusion, and then complain to the security guard that they are frightened of being locked in.
Averted in The Bourne Supremacy.

Landry: Have you locked down the area? (Bourne has just escaped)
CIA Mook: This is Italy, they don't do lockdown.

Literature

Done in the Agent Pendergast novel The Relic, with disastrous results.
Blind Lake begins with the entirety of the titular town being put under lockdown for an unknown reason.
Happens for months to the city of Oran in The Plague, due to bubonic plague. The novel explores the psychological effects on the people within, who become pretty much depressed and gloomy.

Live Action TV

The Lone Gunmen used automatic fire doors in the improvised lockdown of a pathogen-contaminated corridor when they made their Heroic Sacrifice at the end of The X-Files.
Scrubs had a quarantine.
- and an Indy Hat Roll
Heroes had a lockdown in Level 5 to keep the bad dudes from getting out.
The lockdown in the hatch in Lost seems to shield the residents with blast shield. The previous Dharma Initiative resident used these shields as maps before the arrival of the protagonists.
24. CTU is locked down during the first season.
- CTU is locked down constantly, but it never seems to do any good actually stopping people from breaking in or out!
Stargate SG-1 has a lockdown protocol, including Stock Footage of the NORAD blast doors closing (see Real Life).
The first (broadcast) episode of The Outer Limits from the '90s had a secure medical experiment lab that could be sealed and sterilized with microwaves.
Spooks has done this twice. First with the VX episode "I Spy Apocalypse", and then with the episode with the crazy former spy, and the Princess Di conspiracy theory story.
In Bones, the boys were sawing a bone that had some fungus in it, resulting in the team being locked down for Christmas in the Jeffersonian lab. It's first time we see Angela's father.
Torchwood had one that activated by reading poetry and could be removed by reading the ISBN number of said poetry anthology. (It Makes Sense in Context)
Star Trek does this a few times.
Happens in Oz (and every other prison drama) when someone gets murdered or the prisoners riot.
Parodied in a Very Special Episode of One Tree Hill where Jimmy Edwards shoots up the school. He doesn't understand how Keith is able to enter the school because...

Jimmy: The school's on lockdown!!!

Happens a few times on Eureka with Global Dynamics.
Purdey gets trapped inside a high-tech building that goes into lockdown in The New Avengers episode "Complex".
Happens in a few episodes My Name Is Earl when Earl is in prison for a crime that Joy committed.

Tabletop Games

City Of The Gods, a part of Dungeons & Dragons Blackmoor series, locks down the corridors if the PCs set off the alarm and appear to either be escaping or have remained in full alert for too long.

Video Games

The vaults in Fallout.
In Sonic Adventure 2, the titular prison of Prison Island is locked down when Tails gets there. Also, the facility that Dr. Eggman breaks into to retrieve the secret weapon goes into lockdown. This time, you see a number of doors closing and hear a voice telling people to close them. (In both cases, the doors that don't succumb to you blowing off the locks open anyway just because you destroyed some G.U.N. robots.)
Mitadake High begins with you in a locked-down school with the killer. It Gets Worse.
Devil Survivor takes place in the "Tokyo Lockdown", things get complicated and bad very quickly.
Periodically in Dead Space, the room Isaac is in goes into "quarantine" lockdown. The lockdown ends when he successfully defeats the Necromorphs that find their way in.

Web Comics

In El Goonish Shive Moperville South school has a "standard lockdown procedure". This means suddenly every door is locked (even ones without locks) and corridors are cut into sectors with Some Kind of Force Field. How can this happen? Because one of the teachers is a wizard.

Web Original

"Mix Up at the Snack Factory".

"Mr. Cheezo, the workers aren't gonna make it out alive."
"Well, I guess we'll have to hire new workers, won't we?"

Western Animation

Young Justice: In "Terrors", Amanda Waller locks down Belle Reve in an attempt to stop the mass breakout.

Real Life

In the U.S., due to the rash of school shootings most schools have a Lockdown procedure that goes into effect if there's any report of a violent criminal or crime in (or even near) the school. All teachers are told to lock their doors until they get the all clear.
US government buildings usually have Lockdown procedures as well, in case of workplace violence or terrorism.
NORAD in Cheyenne Mountain has a lockdown procedure to isolate itself from the world, including sealing a huge blast door.
In the first quarter of 2020, the novel infectious disease COVID-19 caused Italy, Spain, France, and parts of China and the United States to enact shelter-in-place orders lasting several weeks.