Pattern of live cells in the game of life which will move continuously diagonally across the field of cells. The pattern is something like this:

 o
  o
ooo

The glider in the above diagram will move downwards and to the right until it hits something. The progress of the glider includes a flip along the diagonal axis of its motion. The development of the glider was the first step in the development of a pattern of finite initial size which would grow infinitely: the glider gun.