GNU Emacs Lisp Reference Manual
8.3: Kinds of Forms
A Lisp object that is intended to be evaluated is called a form.
How Emacs evaluates a form depends on its data type. Emacs has three
different kinds of form that are evaluated differently: symbols, lists,
and ``all other types''. This section describes all three kinds,
starting with ``all other types'' which are self-evaluating forms.