The singular misstep: why "a women" is not correct

What kind of error is it?

It is a grammatical error involving the use of an incorrect indefinite article with a plural noun.

Why do people make this mistake?

People may mistakenly use "a women" because they confuse the plural form "women" with the singular form "woman", or they may not be fully aware of the singular and plural distinction between "woman" and "women".

What is correct?

The correct form is "a woman". "A" is an indefinite article used with singular nouns, so it should only be paired with the singular noun "woman".