A horse and sheep? One's above and below! (7)
I believe the answer is:
anagram
'one's above and below' is the definition.
I can't tell whether this defines the answer.
'a horse and sheep?' is the wordplay.
'horse' becomes 'nag' (term for an old horse).
'and' means one lot of letters go next to another.
'sheep?' becomes 'ram' (male sheep).
'a'+'nag'+'ram'='ANAGRAM'
Can you help me to learn more?
(Other definitions for anagram that I've seen before include "characters on the move" , "Word rearranged from the letters of another" , "One way to clue" , "Word(s) rearranged to form others" , "Hedonism for Sondheim" .)