Everyone at the back of hotel room (4)
I believe the answer is:
hall
'room' is the definition.
(hall is a kind of room)
'everyone at the back of hotel' is the wordplay.
'everyone' becomes 'all' (all people).
'at the back of' says to put letters next to each other.
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'all' put after 'h' is 'HALL'.
(Other definitions for hall that I've seen before include "Large public building" , "Auditorium" , "College dining room" , "Large meeting room" , "Building used for public assembly" .)