Run round Ireland in shorts on vacation (6)
I believe the answer is:
series
'run' is the definition.
(both can mean a sequence of things)
'round ireland in shorts on vacation' is the wordplay.
'round' says the letters should be written backwards.
'ireland' becomes 'eire' (poetic name for Ireland).
'in' is an insertion indicator.
'on vacation' means to remove the middle letters (after the inside letters have vacated the word).
'shorts' with its middle taken out is 'ss'.
'eire' going within 'ss' is 'seires'.
'seires' written backwards gives 'SERIES'.
(Other definitions for series that I've seen before include "Progression of things" , "Set of things in line" , "Number of similar things arranged in order" , "Set of TV programmes" , "Progression or sequence" .)