What is Base Fee?

Legal Definition
A base fee is an interest in real property that has the potential to last forever, provided a specified contingent event does not take place. For example, a grantee might be given an interest in a piece of land, "as long as the land is not used for any illegal purposes."
-- Wikipedia
Legal Definition
English law. A tenure in fee at the will of the lord. This was distinguished from socage free tenure. See Co. Litt. 1, 18.
-- Bouviers Law Dictionary
Legal Definition
A determinable or qualified fee; an estate having the nature of a fee, but not a fee simple absolute.
-- Black's Law Dictionary
Legal Definition
In English law. An estate or fee which has a qualification subjoined thereto, and which must be determined whenever the qualification annexed to it is at an end. 2 Bl. Comm. 109. Wiggins Ferry Co v. Railroad Co., 94 111. 93; Camp Meeting Ass'n v. East Lyme, 54 Co.nn. 152, 5 Atl.1 849.
-- Black's Law Dictionary
Legal Definition
A qualified fee determinable upon the ending of the qualification. See 94 111. 83.
-- Ballentine's Law Dictionary