Definition of Firma
In old English law, the contract of lease or letting; also the rent (or farm) reserved upon a lease of lands, which was frequently payable in provisions, but sometimes in money, in which latter case it was called "alba firma,” white rent.
A tribute or custom paid towards entertaining the king for one night.
That's the definition of Firma in Black's Law Dictionary 6th Edition. Courtesy of Cekhukum.com.