Full Idea
We call a 'collection' of jewels a 'group' term. Several random musicians are unlikely to be an orchestra. If they come together regularly in a room to play, such conditions are constitutive of an orchestra.
Gist of Idea
A 'group' is a collection with a condition which constitutes their being united
Source
Peter Simons (Parts [1987], 4.4)
Book Reference
Simons,Peter: 'Parts: a Study in Ontology' [OUP 1987], p.146
A Reaction
Clearly this invites lots of borderline cases. Eleven footballers don't immediately make a team, as followers of the game know well.