Defined in terms of itself. Recursion is how a small rule reaches an unbounded depth.
Latin recurrere (to run back): re- (back) + currere (to run); a recursive thing runs back into its own definition, reaching an unbounded depth from one small rule applied to itself.
Defined in terms of itself. The root's running-back is precise: recursion is how a small rule reaches an unbounded depth, one return to itself at a time.