Lisp, which stands for "LISt Processing," is a programming language. Lisp is the second-oldest high-level programming language still in common use, after Fortran. Lisp has changed since its early days, and many dialects have existed over its history. Today, the best-known general-purpose Lisp dialects are Common Lisp, Scheme, Racket and Clojure.

Lisp was invented by John McCarthy in 1958 while he was at the Massachusetts Institute of Technology (MIT).

McCarthy published its design in a paper in Communications of the ACM in April 1960, entitled "Recursive Functions of Symbolic Expressions and Their Computation by Machine, Part I".

At its core, Lisp treats code and data interchangeably, representing both in the form of lists. In Lisp, a program is expressed as a series of nested lists, known as S-expressions (Symbolic Expressions). Each S-expression consists of an operator (a function or an operator symbol) followed by zero or more operands.

One of the distinguishing features of Lisp is its support for homoiconicity, which means that Lisp code is written in the same structure as Lisp data. This allows Lisp programs to be manipulated and transformed as data, enabling powerful metaprogramming capabilities. Lisp supports the creation and manipulation of functions as first-class objects, allowing functions to be passed as arguments to other functions, returned as results, and stored in data structures.

Lisp provides a rich set of built-in functions and macros, which can be combined and extended to solve a wide range of programming problems. It also offers a flexible and dynamic type system, allowing programmers to dynamically define and modify data types at runtime.

Lisp has influenced the development of many other programming languages and has been used in various domains, including artificial intelligence research, language processing, and symbolic computation. Common Lisp and Scheme are two of the most widely used dialects of Lisp, each with its own set of features and design philosophies.