For example, very old packed theatre (5)
I believe the answer is:
savoy
'theatre' is the definition.
(I've seen this before)
'for example very old packed' is the wordplay.
'for example' becomes 'say' ('say' can be used to introduce an example).
'very' becomes 'v' (abbreviation).
'old' becomes 'o' (abbreviation).
'packed' means one lot of letters goes inside another (some letters are packed into others).
'v'+'o'='vo'
'say' enclosing 'vo' is 'SAVOY'.
(Other definitions for savoy that I've seen before include "Dense cabbage" , "Variety of cabbage" , "Cabbage; hotel" , "area of France" , "Type of cabbage - London theatre" .)