In canon law, commendam (or in commendam) was a form of transferring an ecclesiastical benefice in trust to the custody of a patron. The phrase in commendam was originally applied to the provisional occupation of an ecclesiastical benefice, which was temporarily without an actual occupant – in contrast to the conferral of a title, in titulum, which was applied to the regular and unconditional occupation of a benefice.
Granting a benefice in commendam became most common with monasteries, and the commendatory abbot drew a portion of the revenue of the monastery, but without fulfilling the duties of the abbot or even residing at the monastery.
Read more about In Commendam: History, Church of England, Etymology