catch some z's

VERB
14 LETTERS · STARTS WITH C

catch some z's is a valid 14-letter word worth 29 points in Scrabble and 31 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
C3A1T1C3H4S1O1M3E1Z10'0S1
3 + 1 + 1 + 3 + 4 + 0 + 1 + 1 + 3 + 1 + 0 + 10 + 0 + 1 =29 PTS
DOUBLE WORD → 58TRIPLE WORD → 87
MEANING

What does catch some z's mean?