cond is a special form in `C source code'.

(cond CLAUSES...)

Try each clause until one succeeds.
Each clause looks like (CONDITION BODY...). CONDITION is evaluated
and, if the value is non-nil, this clause succeeds:
then the expressions in BODY are evaluated and the last one's
value is the value of the cond-form.
If a clause has one element, as in (CONDITION), then the cond-form
returns CONDITION's value, if that is non-nil.
If no clause succeeds, cond returns nil.