Without men, girls out dancing aren't happy, oddly (3,5)
I believe the answer is:
hen party
'without men girls out' is the definition.
I can't tell whether this defines the answer.
'dancing aren't happy oddly' is the wordplay.
'dancing' indicates an anagram.
'oddly' indicates alternate letters.
The alternating letters of 'happy' are 'hpy'.
'arent'+'hpy'='arenthpy'
'arenthpy' is an anagram of 'HEN-PARTY'.
Can you help me to learn more?
(Other definitions for hen party that I've seen before include "Female-only gathering" , "Females celebrating" , "occasion lacking men" , "Event to which stags are not invited" , "Women's gathering (colloq.)" .)