Belong to or constitute the smaller group or number. The mathematical concept is simply less than half. It is a subset of a group consisting of less than half of the group.  The amount or number by which one aggregate is less than all other aggregates with which it is contrasted. 
Minority interest, non-controlling interest, refers to the portion of a subsidiary corporation's stock that is not owned by the parent corporation. The magnitude of the minority interest in the subsidiary company is an ownership interest less than 50% of the voting interest. 
1530s, "condition of being smaller, that of "smaller number or part" is from 1736.