Old Maid

"Always being one. Never being two. Re-arrange the furniture, There's nothing else to do. Keep an empty house. Watch your brothers wed. Dream an empty dream at night Upon an empty bed. Old maid! Old maid!"

- Lizzie, 110 in the Shade, "Old Maid"

When a female character reaches a certain vaguely-defined age threshold, she will eventually be subjected to the most terrible of insults: "Old Maid". The underlying assumption is, of course, that a woman's value exists only in how successfully she serves and pleases her husband and family, so a woman who is unable to snag a husband is a pathetic worthless failure at life who deserves contempt and ridicule, particularly in older stories from times where traditional gender roles were more strongly enforced. A woman doesn't even have to be called an old maid outright to be threatened; even the hint that someday she might become an old maid - usually because she's not acting in a sufficiently conformist way - is enough to make her either conform or fall into despair.

The insult is still used today, but mostly as a generic inflammatory comment towards women that the speaker doesn't like. Reference will often be made to cats, homely appearance, unlikable demeanor, loneliness, and uselessness. Nosy parents who are wanting for grandkids or are worried about their child's happiness are a rife source of this, as well.

The Spear Counterpart would be "confirmed bachelor", which is usually equated to either eccentricity or closeted homosexuality, although the pressure on women to marry and breed is typically worse.

Old Maid is a parent trope to the following subtropes:
 * Christmas Cake: Old Maids forced to deal with personal or familial angst pertaining to the mostly outdated Japanese cultural idea that a woman is unmarriageable after the age of 25.
 * Maiden Aunt: Old Maids that have remained unmarried and (theoretically) virginal into their twilight years, who instead dote on their siblings' children.

All other examples should be listed here.

Film
"George Bailey: Please, Clarence, where's my wife? Tell me where my wife is. Clarence: You're not going to like it, George. George Bailey: Where is she? What happened to her? Clarence: She became an old maid. She never married... George Bailey: [desperate] Where is she? WHERE IS SHE? Clarence: She's... she's just about to close up the library!"
 * The title character in the 1930s film The Old Maid.
 * Katherine Hepburn fit this trope in at least three different leading roles: The African Queen, Summertime and The Rainmaker.
 * Toula of My Big Fat Greek Wedding is only 30, but her parents seem to think she needs to get married right away.
 * George's wife Mary, in an alternative timeline in It's a Wonderful Life (1946) in which George was never born, meets an indescribably horrific fate:

Literature

 * Charlotte of Pride and Prejudice. This concern only really shows up when Elizabeth objects to Charlotte marrying Mr. Collins under the assumption she's doing it to help Elizabeth's family. Charlotte tells Elizabeth point blank that she [Charlotte] is a 27-year-old single woman with no prospects and no family—the fact that the marriage also helps solve a problem of the Bennetts is only an added incentive.
 * On her eighteenth birthday, Bella Swan has nightmares that she has turned into an ancient lady and her forever-young vampire boyfriend Edward won't love her anymore will keep loving her and treating her just the same. (Visualize a world-class handomse young man tending to an extremely old woman in a wheelchair, and adolescent, utterly lovestruck expression on his face as he gently caters to her every needs while whispering the cheesiest, kindest sincerest terms of endearment...)
 * Avoiding becoming an Old Maid is the motivation of Irma Prunesquallor in Gormenghast. She marries an eighty-six year old man out of desperation, meeting him after holding a party with no women invited, wherein the only invitees were hopelessly pathetic professors of the castle's school.
 * Washington Square and its film version The Heiress play with this trope and end up being one of the few works to portray it positively; the main character never marries her Gold Digger love interest or anyone, and is shown to embrace spinsterhood and be confident in herself in a way she never was when she had to worry about the prospects of marriage.
 * Subverted believably in the Napoleonic era, by Captain Jane Roland in Temeraire, a single mother and dragon rider who refuses to marry a man whom she's about as fond of as she can be of anyone not her daughter or her dragon—partially because of the norms of the day, as she outranks him and she certainly couldn't take a vow to obey him, but also because she's not really interested, though she is flattered.
 * Bridget Jones considers herself to be one.
 * Alix Crown in Quill's Window is an especially blatant example, as she is attractive and wealthy in addition to being single at twenty-five. Incidentally, she does have a good reason for this, as legally she would stand to lose many of her legal rights if she were to get married.

Live-Action TV

 * On The Dick Van Dyke Show, all of Sally's man chasing was due to her fear of becoming an Old Maid. During the run of the show the actress (and by extension the character) turned 40, which even now is considered pretty old for a never-been-married woman who doesn't want to stay unmarried.
 * At least one character in Sex and the City obsessed over becoming an old maid when she hit her late 30s unmarried.
 * Considering Desperate Housewives stars characters that all seem to be constantly fluctuating between married and single in their mid 40's. This either averts the trope or plays it straight with everyone rapidly seeking relationships to avoid this.

Tabletop Games

 * In the card game of the same name, the point is to avoid being stuck with the Old Maid card, the only unmatched one in the deck.

Theatre

 * Larita of Easy Virtue. She and John like to tease eachother about the age difference; he jokingly refers to her as "Grandma".
 * Lizzie in The Rainmaker and its musical adaptation 110 in the Shade is 27 years old, and has had no luck in finding suitors. When Noah tells Lizzie she's going to be an old maid, the words drive her numb with fear before the thought of her brothers marrying one day and her being a Maiden Aunt to their children sends her flying into a hysterical despair.
 * Parodied in the Li'l Abner musical, which gives Daisy Mae the song "I'm Past My Prime," lamenting that she's an old maid at 17. Apparently in the Deep South girls are supposed to be married at an even younger age.
 * In Hello, Dolly!, Ermengarde is driven to tears when her uncle, Horace Vandegelder, won't let her marry her boyfriend. Her reason? "I'm seventeen and in another year, I'll be an old maid!" Mr. Vandegelder replies that if she turns out to be an old maid, he cut her off without a cent.

Web Comics

 * In Sinfest, Monique suffers a brief panic attack over this fate -- and gets over it.

Western Animation

 * Miss Censordoll of Moral Orel.
 * Miss Prissy from Looney Tunes. Many of her appearances involve her trying to snag Foghorn Leghorn as a husband, by hook or by crook. Or by rolling pin.

Real Life
Historical examples only, please - otherwise, this would be Too Common to Trope.
 * Elizabeth I of the United Kingdom, the virgin queen. If she married in that era, she stood to lose throne and kingdom to her eventual spouse.