Corrodians were in essence pensioners who lived in monasteries

Monastery

Monastery denotes the building, or complex of buildings, that houses a room reserved for prayer as well as the domestic quarters and workplace of monastics, whether monks or nuns, and whether living in community or alone .Monasteries may vary greatly in size – a small dwelling accommodating only...

 or nunneries. They were usually well-to-do elderly lay people who paid or were sponsored for accommodation and food for the rest of their lives. This payment might be in cash but would more usually be by donating land to the abbey

Abbey

An abbey is a Catholic monastery or convent, under the authority of an Abbot or an Abbess, who serves as the spiritual father or mother of the community.The term can also refer to an establishment which has long ceased to function as an abbey,...

in question. If they were men with no heirs, the whole estate could be granted to the abbey; otherwise they might 'retire' from the running of their estates and leave that to their heirs, but apportion a part that was not entailed for the abbey.
This was a way for abbeys to gain income, especially in their later days in England, when their numbers were in decline so they had space to accommodate pensioners and less money coming as dowers from new entrants to the orders.