lambda lambda-list ⟦ {declaration}* | documentation  ⟧ {form}*

lambda-list — an ordinary lambda list.

declaration — a declare expression; not evaluated.

documentation — a string; not evaluated.

form — a form.

A lambda expression is a list that can be used in place of a function name in certain contexts to denote a function by directly describing its behavior rather than indirectly by referring to the name of an established function.

Documentation is attached to the denoted function (if any is actually created) as a documentation string.

function, documentation, Section 3.1.3 (Lambda Expressions), Section 3.1.2.1.2.4 (Lambda Forms), Section 3.4.11 (Syntactic Interaction of Documentation Strings and Declarations)

The lambda form

((lambda lambda-list . body) . arguments)

is semantically equivalent to the function form

(funcall #'(lambda lambda-list . body) . arguments)