I'm running into a bit of a snag with my work, simply because there's at least a month of setup and backstory that contribute to the beginning of the story. There's also an issue of unfamiliar terminology that I'm using, and I'm not sure when I should define those terms for the reader. For instance, the primary unfamiliar term is "Reanimate" (as a noun). In the context in which I've used it in the story thus far, all the reader knows is that there are these people who are called Reanimates, and they're unpleasant folks. Beyond that, the reader has no idea how they came about or what their deal is. The Reanimates are the reason for martial law, which has collapsed at the start of the story. Obviously, since it just now collapsed as of the story's beginning, its effects will still be seen. However, I'm not sure whether I should give the reader one big chunk that lays it all out, or give it in pieces. My instinct is to offer little nibbles here and there as they're pertinent to the story, but I'm wondering if that will lead to the reader's frustration that they're slowly figuring everything out.