Some functions, such as concat, + or *, take any
number of arguments. (The * is the symbol for multiplication.)
This can be seen by evaluating each of the following expressions in
the usual way. What you will see in the echo area is printed in this
text after ‘⇒’, which you may read as “evaluates to”.
In the first set, the functions have no arguments:
(+) ⇒ 0 (*) ⇒ 1
In this set, the functions have one argument each:
(+ 3) ⇒ 3 (* 3) ⇒ 3
In this set, the functions have three arguments each:
(+ 3 4 5) ⇒ 12 (* 3 4 5) ⇒ 60