What is Dark Matter?

"The standard cultural framing of dark matter tends to treat it as a known scientific substance."https://spacedaily.com/d-most-of-the-matter-in-the-universe-has-never-been-observed-directly-and-the-existence-of-dark-matter-is-essentially-a-placeholder-name-for-the-gap-between-what-we-can-see-and-what-the-math-requires/