GNU Emacs Lisp Reference Manual

Chapter 27: Positions

A position is the index of a character in the text of a buffer. More precisely, a position identifies the place between two characters (or before the first character, or after the last character), so we can speak of the character before or after a given position. However, we often speak of the character ``at'' a position, meaning the character after that position.

Positions are usually represented as integers starting from 1, but can also be represented as markers---special objects that relocate automatically when text is inserted or deleted so they stay with the surrounding characters. See Markers.