Use of other name or alias

How can I refer to hardware PORTC by a more descriptive term. In my case I would like to call it RegSel.

Can I do this with a # define?

Don't.

Whatever you're doing, you probably don't need the speed required by a direct port write. If you use digitalWrite() your program will function correctly on all Arduinos, including those that haven't been invented yet. If you use PORTC then your hardware is unnecessarily constrained.

You can create a reference to it.

auto& RegSel = PORTC;