Salted part of a margarita glass (3)
I believe the answer is:
'salted part of a margarita glass' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rim that I've seen before include "Flange" , "Brim, edge" , "Raised edge of a round object" , "An edge, canyon or cup" , "Circular outer edge" .)