What is "galvanic couple"

Couple \Cou"ple\ (k[u^]p"'l), n. [F. couple, fr. L. copula a bond, band; co- + apere, aptum, to join. See Art, a., and cf. Copula.]

1. That which joins or links two things together; a bond or tie; a coupler. [Obs.]

   It is in some sort with friends as it is with dogs in couples; they should be of the same size and humor.
   --L'Estrange.

   I'll go in couples with her.
   --Shak.

2. Two of the same kind connected or considered together; a pair; a brace. ``A couple of shepherds.''
   --Sir P. Sidney. ``A couple of drops''
   --Addison. ``A couple of miles.''
   --Dickens. ``A couple of weeks.''
   --Carlyle.

   Adding one to one we have the complex idea of a couple.
   --Locke.

   [Ziba] met him with a couple of asses saddled.
   --2 Sam. xvi. 1.

3. A male and female associated together; esp., a man and woman who are married or betrothed.

   Such were our couple, man and wife.
   --Lloyd.

   Fair couple linked in happy, nuptial league.
   --Milton.

4. (Arch.) See Couple-close.

5. (Elec.) One of the pairs of plates of two metals which compose a voltaic battery; -- called a voltaic couple or galvanic couple.

6. (Mech.) Two rotations, movements, etc., which are equal in amount but opposite in direction, and acting along parallel lines or around parallel axes.

   Note: The effect of a couple of forces is to produce a rotation. A couple of rotations is equivalent to a motion of translation.

n. 1 The corrosive cell formed when two different metals are separated by an electrolyte, or the corrosion produced by this effect. 2 The pair of plates (made of different metals or other conductive materials) which form a voltaic cell in a battery.