What is Perpetual Curacy?

Legal Definition
The office of & curate in a parish where there is no spiritual rector or vicar, but where a clerk (curate) is appointed to officiate there hr the impropriator. 2 Burn, Ecc. Law, 55. The church or benefice filled by a curate under these circumstances is also so called.
-- Black's Law Dictionary
Legal Definition
One wherein all the titles are appropriated, and no vicarage endowed, but instead thereof a perpetual curate is appointed by the appropriator. See 1 Bl. Comm. 394.
-- Ballentine's Law Dictionary