single word requests - What do you call a 'noun' with a (s) suffix e.g. parent(s)?

Is there a term for use of a combined singular / plural like parent(s)?

For example:

Do not assume there are two parents when you pen the letter regarding baby Bob;
use _____ instead.

or

use the _____ approach instead?

I am not asking if parent(s) is good style - that is separate issue.
I have seen a question asking how to add a possessive 's to it but that is separate problem.
I googled for this but am not sure what to even search for.

Answer

Many sites refer to this convention as the parenthetical plural.

For example, at the Grammarphobia Blog, the American Medical Association, and the Chicago Manual of Style.

This site discusses the merit of "parenthetical plural," and points out that

The Gregg Reference Manual calls them "plural endings in parentheses."

You might also find them called optional plurals.