Hi, Yatima co-author here, this paragraph refers broadly to static dependent types, like in Idris, but I described them as "first-class-types" here because I thought it sounded more accessible. Also, becase at the type-level Yatima types are ordinary values, so there's an analogy that can be drawn with first-class functions.

But it seems from this thread this caused confusion, so I'll update the README shortly to clarify.