The Collaborative International Dictionary of English v.0.48:

ampere-turn \ampere-turn\, Ampere turn \Amp[`e]re turn\ (Elec.)
   A unit of magnetomotive force equal to the product of one
   complete convolution (of a coiled conductor) into one
   amp[`e]re of current; thus, a conductor having five
   convolutions and carrying a current of half an amp[`e]re is
   said to have 21/2 amp[`e]re turns. The magnetizing effect of
   a coil is proportional to the number of its amp[`e]re turns.
   [Webster 1913 Suppl.]