According to the glossary in Super System by Brunson:

Set: A term used to describe Trips or Fours (Four-of-a-kind), as in a 'Set of trips'.

According to the glossary in The Theory of Poker by Sklansky:

Set: Three-of-a-kind. The term is used particularly in hold 'em.

None of them say it has to be a pocket pair combined with the board.

Endastory.