Grand adult events including Queen conventions (10)
I believe the answer is:
gatherings
'conventions' is the definition.
(I've seen this before)
'grand adult events including queen' is the wordplay.
'grand' becomes 'g' (G is short for grand as in a thousand).
'adult' becomes 'a' (abbreviation).
'events' becomes 'things' (thing is a kind of event).
'including' means one lot of letters goes inside another.
'queen' becomes 'ER' (abbreviation for Elizabeth Regina).
'things' going around 'er' is 'therings'.
'g'+'a'+'therings'='GATHERINGS'
(Another definition for gatherings that I've seen is " conventions".)