closed string

13 LETTERS · STARTS WITH C

closed string is a valid 13-letter word worth 16 points in Scrabble and 20 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS

C3L1O1S1E1D2S1T1R1I1N1G2

3 + 1 + 1 + 1 + 1 + 2 + 0 + 1 + 1 + 1 + 1 + 1 + 2 =16 PTS

DOUBLE WORD → 32TRIPLE WORD → 48

MEANING

What does closed string mean?