Guitar pick
A guitar pick is a plectrum
A plectrum is a small flat tool used to pluck or strum a stringed instrument. For hand-held instruments such as guitars and mandolins, the plectrum is often called a pick, and is a separate tool held in the player's hand...

 used for guitar
The guitar is a plucked string instrument, usually played with fingers or a pick. The guitar consists of a body with a rigid neck to which the strings, generally six in number, are attached. Guitars are traditionally constructed of various woods and strung with animal gut or, more recently, with...

s. A pick is generally made of one uniform material; examples include plastic, nylon, rubber, felt
Felt is a non-woven cloth that is produced by matting, condensing and pressing woollen fibres. While some types of felt are very soft, some are tough enough to form construction materials. Felt can be of any colour, and made into any shape or size....

, tortoiseshell
Tortoiseshell material
Tortoiseshell or tortoise shell is a material produced mainly from the shell of the hawksbill turtle, an endangered species. It was widely used in the 1960s and 1970s in the manufacture of items such as combs, sunglasses, guitar picks and knitting needles...

, wood, metal, glass, and stone. They are often shaped in an acute isosceles triangle
A triangle is one of the basic shapes of geometry: a polygon with three corners or vertices and three sides or edges which are line segments. A triangle with vertices A, B, and C is denoted ....

 with the two equal corners rounded and the third corner rounded to a lesser extent.
Pick shapes started with guitarists shaping bone, shell, wood, cuttlebone, metal, amber, stone or ivory to get the desired shape.