School I'm describing second division (6)
I believe the answer is:
schism
'division' is the definition.
(I know that schism is a type of division)
'school i'm describing second' is the wordplay.
'school' becomes 'sch' (abbreviation).
'describing' means one lot of letters goes inside another (describe can mean to form the outline of).
'second' becomes 's' (common abbreviation).
'im' enclosing 's' is 'ism'.
'sch'+'ism'='SCHISM'
(Other definitions for schism that I've seen before include "Splitting of a Church" , "Formal separation of a church into two churches" , "Split based on opposing beliefs" , "Split, rift" , "Breach within a Chruch" .)