An s-expression, also known as a sexpr or sexp, is a way to represent a nested list of data. It stands for "symbolic expression," and it is commonly encountered in the Lisp programming language and variants of Lisp such as Scheme, Racket, and Clojure. These programming languages use s-expressions to represent the computer program, and the program's data.
For example, the simple mathematical expression "five times the sum of seven and three" can be written as a s-expression with prefix notation. In Lisp, the s-expression might look like the example below.
(* 5 (+ 7 3))