The OED is more interesting:

A forest assembly held three times a year in accordance with the Forest Charter of 1217, probably originally to enable the forest officers to superintend the depasturing of pigs in the king's woods in the autumn and the clearance of the forest of cattle and sheep while the deer were fawning in the summer; later, applied vaguely or generically to courts of attachment, inquisition, etc.

Literally a meeting of swineherds.