Source : Webster's Revised Unabridged Dictionary (1913)

Corrugation \Cor`ru*ga"tion\ (k?r`r?-g?"sh?n), n. [Cf. F.
   corrugation.]
   The act corrugating; contraction into wrinkles or alternate
   ridges and grooves.

Source : WordNet®

corrugation
     n 1: a ridge on a corrugated surface
     2: the act of shaping into parallel ridges and grooves