What is Quantum Tenens Domino Ex Homagio, Tantum Dominus Tenenti Ex Dominio Debet Praeter Solam Reverentiam; Mutua Debet Esse Dominii Et Homagii Fidelitatis Connexio?

Legal Definition
Co. Litt. 64. As much as the tenant by his homage owes to his lord, so much is the lord, by his lordship, indebted to the tenant, except reverence alone; the tie of dominion and of homage ought to be mutual.
-- Black's Law Dictionary