Full Idea
Roughly, numbers, sets and propositions are assumed to be abstract particulars, while properties, including qualities and relations, are usually thought to be universals.
Gist of Idea
Numbers, sets and propositions are abstract particulars; properties, qualities and relations are universals
Source
Dale Jacquette (Ontology [2002], Ch. 9)
Book Reference
Jacquette,Dale: 'Ontology' [Acumen 2002], p.209
A Reaction
There is an interesting nominalist project of reducing all of these to particulars. Numbers to patterns, sets to their members, propositions to sentences, properties to causal powers, relations to, er, something else.