A teacher may call it a set of notes (8)
I believe the answer is:
register
'a teacher may call it a' is the definition.
I can't tell whether this defines the answer.
'set of notes' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'set' is 'ste' which is located in the answer.
'notes' could be 'eg' (two musical notes) and 'eg' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for register that I've seen before include "Official record of names etc." , "To express" , "Record book" , "See 1" , "(Put one's name down on) list" .)