The Collaborative International Dictionary of English v.0.48:

Toggle switch \Tog"gle switch`\, n.
   1. (Elec.) an electrical switch operated by pushing a lever
      through a small angle of deflection. The lever has a
      spring which returns it to its original position after the
      pressure applied by the operator is released.
      [PJC]

   2. (Computer programming) A mechanism for acquiring input
      from an operator, such that taking some action (such as
      pressing a function key on a keyboard) will cause a
      program variable to take a new value. The values are
      usually changed in cyclic fashion, so that a certain
      number of activations of the toggle returns the variable
      to its initial value. When there are two values to the
      variable, each activation of the toggle causes the
      variable to assume the alternate value.
      [PJC]
      [1913 Webster]

WordNet (r) 3.0 (2006):

toggle switch
    n 1: a hinged switch that can assume either of two positions
         [syn: toggle switch, toggle, on-off switch, on/off
         switch]