What is Quasi Seisin?

Legal Definition
A term applied to the possession which a copyholder has of the land to which he has been admitted. The freehold in copyhold lands being in the lord, the copyholder cannot have seisin of them in the proper sense of the word, but he has a customary or quasi seisin analogous to that of a freeholder. Williams, Seis. 126; Sweet.
-- Black's Law Dictionary