interface – What is the term for a numeric input field of a specific format?

I am trying to come up with some common terms and definitions that are
suitable to use for specification or design documents

I don’t think i can come-up with a better suggestion than the one you mentioned “formatted’ numeric input field” Its the best possible outcome and I don’t think you should worry too much because its long, though you can make adjustments when this is included in documentation. For example:

Formatted Input Field (numeric) where numeric becomes an additional attribute!

The most important thing is that its understandable and clear and given that it needs to go into documentation for an audience that might not be well versed in technical knowledge, the logic should be that descriptivness beats conciseness

If we look at this purely from labelling point of view then your suggestion is the least ambiguous and most descriptive of all alternatives I have seen so far and would be the most useful for a larger audience.

Input Field vs Input Type or Input Element:

If you are to ask as many people in your target audience to define this element than I am sure that the majority will use “input field ” or “input box” its a hypothesis but could be easily tested:)

The term “Input Field” will work well as opposed to “Input Type” or “Input Element” these being more ambiguous and could trigger further inquires when used in design documentation. Also the term “Input Field” focuses on a unique element with a descriptor “field” as opposed to using input or inputs only, which could be confused with other form controls.

Formatted Input Fields:

The term “formatted” is both descriptive, unambiguous and its meaning is widely understood which will help convey how the input field works as opposed to “fixed” which is very restrictive and unfamiliar and could lead readers to question it further.

In addition,the term “formatted” denotes the act of arranging or put into a format regardless of how this is done which in my opinion describes: What the field is rather than how it works.