spore sac

NOUN /spoʊr_sæk/
9 LETTERS · STARTS WITH S

spore sac is a valid 9-letter word worth 12 points in Scrabble and 14 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
S1P3O1R1E1S1A1C3
1 + 3 + 1 + 1 + 1 + 0 + 1 + 1 + 3 =12 PTS
DOUBLE WORD → 24TRIPLE WORD → 36
MEANING

What does spore sac mean?