Finale where nothing divides 100,500 by 1 (4)
I believe the answer is:
coda
'finale' is the definition.
('coda' can be a synonym of 'finale')
'nothing divides 100500 by 1' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'divides' indicates putting letters inside.
'100500' becomes 'cd' (CD is 100,500 in Roman numerals).
'by' says to put letters next to each other.
'1' becomes 'a' (both can mean one).
'o' going within 'cd' is 'cod'.
'cod'+'a'='CODA'
'where' acts as a link.
(Other definitions for coda that I've seen before include "Ending of musical piece" , "Final movement" , "Closing section of a musical composition" , "Novel ending" , "End of movement" .)