The Linkspages at Larsdatter.com

A harrow is an agricultural implement that has a heavy frame set with teeth. The farmer uses a horse to drag the harrow over plowed land to break up clods of dirt, take out weeds, and cover the seeds.

From Walter of Henley's Husbandry:

See also Medieval Farming and Technology.

The term “harrow” also refers to a parchment-maker's frame (e.g., “He was thus sprede o-brode one þe crosse more straite þan any parchemyne-skyne es sprede one þe harowe,” The Privity of the Passion c. 1440).