go-between

NOUN /ɡoʊbɪ,twin/
10 LETTERS · 2 SYLLABLES · STARTS WITH G

go-between is a valid 10-letter word worth 15 points in Scrabble and 18 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
G2O1-0B3E1T1W4E1E1N1
2 + 1 + 0 + 3 + 1 + 1 + 4 + 1 + 1 + 1 =15 PTS
DOUBLE WORD → 30TRIPLE WORD → 45
MEANING

What does go-between mean?