You're right that his makes deleted definition and deleted function less redundant, but is this really a necessary change?

What does this improve? Is the current wording problematic in some way?

Yeah, I don't see a problem with the current wording. It doesn't really matter whether a given function is explicitly declared as defaulted and implicitly deleted, or explicitly declared as deleted, or implicitly declared and deleted, all of those are covered by [dcl.fct.def.delete] and are all deleted functions. If we need to distinguish between those cases elsewhere, we can do so. But for the purposes of defining the term "deleted function" it doesn't matter.

How do you interpret the phrase implicitly defined as deleted, this term is not defined in the current wording.

One that is defined as deleted without you actually saying = delete. It doesn't actually matter whether that's because you say =default and the compiler defines it as deleted, or you don't declare it at all and the compile implicitly declares it and deletes it ... both cases are deleted functions anyway. So the definition of "deleted function" is ok.

It doesn't actually matter whether that's because you say =default and the compiler defines it as deleted,

This is a function with a deleted definition, indeed, a deleted function

or you don't declare it at all and the compile implicitly declares it and deletes it ... both cases are deleted functions anyway.

This is the implicitly declared function that is defined as deleted, which is defined in clauses [class].

For the phrase a function that is implicitly defined as deleted, if there is no specific definition, it should refer to

1. An explicitly-defaulted function that is defined as deleted
2. An implicitly declared function that is defined as deleted

The first one is partially covered by

a function with a deleted definition

as per [dcl.fct.def.delete] p1.

It is an improvement if we define the deleted function as:

A deleted function is a function with a deleted definition or an implicitly declared function that is defined as deleted.