The Collaborative International Dictionary of English v.0.48:

Heft \Heft\, n.; G. pl. Hefte. [G.]
   A number of sheets of paper fastened together, as for a
   notebook; also, a part of a serial publication.

         The size of "hefts" will depend on the material
         requiring attention, and the annual volume is to cost
         about 15 marks.                          --The Nation.
   [Webster 1913 Suppl.]