1
general::
1. Sleep at home, as opposed to one's place of employment, as in We have a full-time nurse for her, but she sleeps out. [Mid-1800s] 2. Sleep away from one's own home, as in She's not here; she's sleeping out.
American Heritage Idioms
2
general::
Phrase(s): sleep out
to sleep outside or away from one’s home. • Can I sleep out tonight? • Didn’t you sleep out last night?
McGrawhill's American Idioms And Phrasal Verbs