sexual union

NOUN /sɛkʃuəl_'junjən/
12 LETTERS · STARTS WITH S

sexual union is a valid 12-letter word worth 18 points in Scrabble and 23 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
S1E1X8U1A1L1U1N1I1O1N1
1 + 1 + 8 + 1 + 1 + 1 + 0 + 1 + 1 + 1 + 1 + 1 =18 PTS
DOUBLE WORD → 36TRIPLE WORD → 54
MEANING

What does sexual union mean?