Fender nuts usually have an arc along their bottom. This mates with a similar curve in the nut slot itself. If you’re installing a new nut, you’ll have to match this radius closely for a good fit.
Find out how…
While most guitars have a single radius along the length of the fingerboard, a compound radius instrument has a radius that gradually increases/flattens as you go further up the neck.
Some players find these a godsend but they do require some different methods to set them up and to perform fretwork on them.