Garters are items of clothing worn around the thighs. They are normally just a few inches in width. They often contain small bells and/or ribbons. In the 19th and 20th centuries, they were used to hold up stockings, but the advent of elastic has made them unnecessary.
The most famous "garter" in English is the Order of the Garter, which traces its history to the Middle English poem Sir Gawain and the Green Knight. In the poem, Gawain accepts a garter from the wife of his host (while resisting her carnal temptations) to save his life and then wears it as a mark of shame for his moral failure and cowardice. King Arthur and his men proclaim it no shame and begin, themselves, to wear the garter to indicate their shared fate. At that point, however, the garter was a larger garment that was used as a foundation.
In Elizabethan fashions, men wore garters with their hose, and colorful garters were an object of display. In Shakespeare's Twelfth Night, "cross braced" garters are an object of some derision. In male fashion, a type of garter for holding up socks has continued as a part of male dress up to the present (although its use is considered somewhat stodgy at present).
As with many items of female undergarments, they are sometimes items of fetish. For this reason they are sometimes worn by exotic dancers.
A garter is often worn by newlywed brides. It is the groom's privilege to remove the garter and toss it to the male guests. The symbolism to deflowering is unambiguous.
