Well-liked youth centre in tree (7)
I believe the answer is:
popular
'well-liked' is the definition.
(similar in meaning)
'youth centre in tree' is the wordplay.
'youth centre' becomes 'u' (middle letter of the word 'youth').
'in' means one lot of letters goes inside another.
'tree' becomes 'poplar tree' (poplar tree is a kind of tree).
'u' placed into 'poplar' is 'POPULAR'.
(Other definitions for popular that I've seen before include "Non-technical" , "Well-liked" , "Trendy" , "Demotic" , "Commonly known" .)