Universities host band in holidays, being unoccupied (7)
I believe the answer is:
vacuous
'unoccupied' is the definition.
(thesaurus)
'universities host band in holidays' is the wordplay.
'universities' becomes 'UU' (an abbreviation for university written twice).
'host' is an insertion indicator (inserted letters are hosted or welcomed).
'band' becomes 'o' (I've seen this in other clues).
'in' is an insertion indicator.
'holidays' becomes 'vacs' (vac is a kind of holiday).
'uu' enclosing 'o' is 'uou'.
'uou' put into 'vacs' is 'VACUOUS'.
'being' acts as a link.
(Other definitions for vacuous that I've seen before include "Lacking intelligent ideas" , "Empty-headed" , "Expressionless" , "Devoid of significance or point" , "Empty; inane" .)