dress down

VERB /drɛs_daʊn/
10 LETTERS · STARTS WITH D

dress down is a valid 10-letter word worth 14 points in Scrabble and 15 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
D2R1E1S1S1D2O1W4N1
2 + 1 + 1 + 1 + 1 + 0 + 2 + 1 + 4 + 1 =14 PTS
DOUBLE WORD → 28TRIPLE WORD → 42
MEANING

What does dress down mean?