"Advowson The right of nomination or presentation to an ecclesiastical benefice. An advowson is held by a patron, who may he an individual or institution, clerical or secular. The patron presents the candidate to the appropriate Bishop for institution and induction, though the nomination may he refused. An advowson is a form of property which may he bought, sold or given away and is subject to civil law. An advowson appendant is one annexed to a manor or estate, an advowson in gross is in the gift of an individual."
From what I can understand it's a right to appoint someone to a church but it still needs the approval of the Bishop and it can be passed down.
"In the year 1555 Rich granted the advowson to Queen Mary, and on her death it was inherited by Queen Elizabeth; who in 1560 regranted it "