06-03-2023-1145 - In computer programming, an S-expression (or symbolic expression, abbreviated as sexpr or sexp)

Tree data structure representing the S-expression (* 2 (+ 3 4))

In computer programming, an S-expression (or symbolic expression, abbreviated as sexpr or sexp) is an expression in a like-named notation for nested list (tree-structured) data. S-expressions were invented for and popularized by the programming language Lisp, which uses them for source code as well as data. 

https://en.wikipedia.org/wiki/S-expression