A normat is a normative category, which is often not even seen as a category at all. For example, it is in mainstream western culture normative to be white, cisgender and heterosexual. Thus a normat woman is a woman who is white, heterosexual, cisgender and so on. Such a woman will typically not be called nomat or white or whatever, she will simply be called a woman.
A normative category that is conceptualized not merely as being normative but as not being a category at all. For example, in a context where it is normative to be white and male, these categories can develop into zero-category by people getting the idea that gender is something that only women have and that skin-color is something that only “people of color” have. (In Swedish: nollkategori)
A lack of intersectionality goes well together with making the normative category invisible. It thus becomes easy to talk about “women” as a concept that actually refers only to white heterosexual women, “people of color” or “muslims” as a concept that actually refers only to heterosexual men of that wider category, and so on.