What is "eval"

Eval \E"val\ ([=e]"val), a. [L. aevum lifetime, age, eternity.] Relating to time or duration. [Obs.]

Etymology 1 n. evaluation Etymology 2

a. (context obsolete English) Relating to time or duration.

In some programming languages, eval is a function which evaluates a string as though it were an expression and returns a result; in others, it executes multiple lines of code as though they had been included instead of the line including the eval. The input to eval is not necessarily a string; it may be structured representation of code, such as an abstract syntax tree (like Lisp forms), or of special type such as code (as in Python). The analog for a statement is exec, which executes a string (or code in other format) as if it were a statement; in some languages, such as Python, both are present, while in other languages only one of either eval or exec is.

Eval and apply are instances of meta-circular evaluators, interpreters of a language that can be invoked within the language itself.