In ordinary terms, right in position (5)
I believe the answer is:
prose
'in ordinary terms' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'right in position' is the wordplay.
'right' becomes 'r' (common abbreviation).
'in' is an insertion indicator.
'position' becomes 'pose' (posing is a kind of positioning).
'r' inserted into 'pose' is 'PROSE'.
Can you help me to learn more?
(Other definitions for prose that I've seen before include "Gossipy talker" , "Text" , "Ropes (anag.)" , "Writings not in verse" , "Literary genre" .)