A sequin () is a small, typically shiny, generally disk-shaped ornament.

Sequins are also referred to as paillettes, spangles, or diamanté (also spelled diamante). Although the words sequins, paillettes, lentejuelas, and spangles can be used interchangeably, diamanté (literally "set with diamonds") is both an adjective and a plural-only noun, which specifically refers to diamond-shaped sequins and can also be used to mean "artificial diamonds", which serve the same purpose as sequins.

In costuming, sequins have a center hole, while spangles have the hole located at the top. Paillettes are typically very large and flat. Sequins may be stitched flat to the fabric, so they do not move, and are less likely to fall off; or they may be stitched at only one point, so they dangle and move easily, catching more light. Some sequins are made with multiple facets, to increase their reflective ability, while others are stamped out with lobes resembling flower petals.