fboundp

(fboundp symbol)

Returns t when symbol names something callable or expandable: a function (built-in or defun), a macro (built-in or defmacro), a special form, or a car/cdr composition like cadr. This matches Common Lisp, where fboundp is true of macros and special operators too.

On the compiled backends a literal quoted argument is decided at compile time with full knowledge (macros and special forms included); a computed argument is checked at runtime against the function registries, which only know real functions — so (fboundp (intern "cond")) is nil in compiled code but t in the interpreter, and defmacro macros are likewise compile-time-only there.