metric capacity unit

NOUN
20 LETTERS · STARTS WITH M

metric capacity unit is a valid 20-letter word worth 31 points in Scrabble and 37 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
M3E1T1R1I1C3C3A1P3A1C3I1T1Y4U1N1I1T1
3 + 1 + 1 + 1 + 1 + 3 + 0 + 3 + 1 + 3 + 1 + 3 + 1 + 1 + 4 + 0 + 1 + 1 + 1 + 1 =31 PTS
DOUBLE WORD → 62TRIPLE WORD → 93
MEANING

What does metric capacity unit mean?