Period that's long when sitting on pole (4)
I believe the answer is:
year
'period' is the definition.
(I know that year is a type of period)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for year that I've seen before include "365 or 366 days" , "Twelvemonth" , "Pupil group" , "Student group" , "Four seasons" .)