Perch or pole fixed in foundation (5)
I believe the answer is:
roost
'perch' is the definition.
(I know that perch can be written as roost)
'pole fixed in foundation' is the wordplay.
I cannot really understand how this works, but
'pole' could be 's' (abbreviation for South, as in South Pole) and 's' is found within the answer.
'foundation' could be 'root' (I've seen this in another clue) and 'root' is found in the remaining letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'or' acts as a link.
Can you help me to learn more?
(Other definitions for roost that I've seen before include "Perch where bird sleeps" , "It's sometimes ruled" , "Temporary resting-place" , "Torso (anag)" , "Where birds rest at night" .)