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.]