Return-to-zero: 1. A common means of encoding data that has two information states called "zero" and "one" in which the signal returns to a rest state during a portion of the bit period. 2. A method of transmitting 1s (flashes of laser light) and 0s (no light) whereby if several 1s are to be transmitted in succession, the laser light turns off in between 1s. It therefore flashes each time it wants to give out a 1, returning to zero light in between 1s. The opposite of a non-return-to-zero (RZ) system.