When a term refers only to a part of the class of things denoted by it, the term is said to be

A term referring only to a part of its class is said to be undistributed.

Distribution turns on whether all members of the term's class are covered.

Here only some members are referred to, not the whole class.

Partial reference leaves the term undistributed.

Covering merely a portion of a term's denotation is the mark of non-distribution.