Meaning of alternate angles

al'ternate an'gles

Pronunciation: [key]
— Geom. Geom.
  1. two nonadjacent angles made by the crossing of two lines by a third line, both angles being either interior or exterior, and being on opposite sides of the third line.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.