Stylus
A stylus (plural: styli) is a writing instrument. It ususally refers to a narrow, elongated staff, similar to a modern ball-point pen. Many styli are slightly curved to be held more easily.
Etymology
The word was borrowed from Latin stilus, that was taken from an Etruscan word that has its origin in Greek stulos (pillar).
Function
Styli are used either for ink work, or used to engrave into metal or clay. In the times of the Romans, stili were often used to engrave wax plates.
"Stylus" is also the term usually used by those in the sound recording industry for what is more commonly called a phonograph or gramophone "needle", used to play back sound on analogue disc records, as well as to record the sound indentations on the master record.
Today, the term "stylus" often refers to an input method usually used in PDAss and Digitizing Tablets. In this method, a stylus that secretes no ink touches a touch screen instead of a finger to avoid getting the natural oil from one's hands on the screen, or produces brushstrokes in a computer screen, respectively.
See also digital ink.