A copyhold was a type of tenancy, where the land was leased from the manor in exchange for set responsibilities. Used widely in England up until the 19th century. Etymologically, the copyholder was one who "held a copy" of this lease.

This historical dictionary, available on google books has a definition on page 127

And the wikipedia article on copyholds gives a good overview.

[Sorry for the wiki link, I know its frowned on, but for a dictionary definition, it's hard to find sources].

Historical Dictionary of Late Medieval England, 1272-1485 edited by Ronald H. Fritze, William Baxter Robison, 2002.