In general use, nil (a contraction of Latin "nihil") means "nothing" or the absence of something. Sometimes nil is used to mean the number zero (0). In programming, nil refers to an empty set or a list containing no entries. In some usages, nil is interchangeable with null. In certain programming languages such as Pascal , SmallTalk , or LISP (list processing), nil represents the absence of an object, or the empty pointer value. In databases, nil refers to an unspecified entry.
The acronym NIL stands for New Implementation of LISP, which has been superseded by CommonLISP. The LISP language and its descendants have been widely used in artificial intelligence ( AI ) programming.