conventional usage

18 LETTERS · STARTS WITH C

conventional usage is a valid 18-letter word worth 23 points in Scrabble and 31 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS

C3O1N1V4E1N1T1I1O1N1A1L1U1S1A1G2E1

3 + 1 + 1 + 4 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 0 + 1 + 1 + 1 + 2 + 1 =23 PTS

DOUBLE WORD → 46TRIPLE WORD → 69

MEANING

What does conventional usage mean?