Parties holding back numerous energetic folk (7)
I believe the answer is:
dynamos
'parties' is the definition.
Although both the answer and definition are plural nouns, I don't see how one could define the other.
'holding back numerous energetic folk' is the wordplay.
'holding' indicates putting letters inside.
'back' says the letters should be written backwards.
'numerous' becomes 'many' (similar in meaning).
'energetic folk' becomes 'dos' (I can't explain this - if you can you should believe this answer much more).
'many' reversed gives 'ynam'.
'ynam' inserted inside 'dos' is 'DYNAMOS'.
Can you help me to learn more?
(Other definitions for dynamos that I've seen before include "Electricity producers" , "Electricity generators or energetic people" , "highly energetic people" .)