A guitar pick (American English) is a plectrum used for guitars. Picks are generally made of one uniform material—such as some kind of plastic (nylon, Delrin, celluloid), rubber, felt, tortoiseshell, wood, metal, glass, tagua, or stone. They are often shaped in an acute isosceles triangle with the two equal corners rounded and the third corner less rounded. They are used to strum chords or to sound individual notes on a guitar.