trim back

VERB
9 LETTERS · STARTS WITH T

trim back is a valid 9-letter word worth 18 points in Scrabble and 21 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
T1R1I1M3B3A1C3K5
1 + 1 + 1 + 3 + 0 + 3 + 1 + 3 + 5 =18 PTS
DOUBLE WORD → 36TRIPLE WORD → 54
MEANING

What does trim back mean?