In semantics, a collective predicate is a predicate that applies to a plurality of things as a whole and not to each of the individual members.
The contrast in the examples shows that gather is a collective predicate because it can only be used as a predicate with a subject that refers to a plurality.
a * John/A boy/Every boy gathered b The boys/John and Mary/The club gathered
Other predicates, such as buy a house or carry the piano upstairs can be used as collective predicates but also as distributive predicates. John and Mary bought a house is therefore ambiguous between a collective reading (they bought the house together) and a distributive reading (they each bought a house).
Link, G. 1983. The logical analysis of plurals and mass terms: a lattice-theoretical approach. In Meaning, use and interpretation of language. Bauerle, R. & Schwarze, C. & von Stechow, A. (eds.), 302-323. Berlin: De Gruyter.