Ultra-tough, misunderstood desert cultures can be a slightly overused trope in fantasy writing, especially alternative world fantasy. They often crop up as the much-needed army for the beset hero, at just the right time, after the hero properly impresses them and meets some ancient prophecy. It might be that the origin of this tendency lies with DUNE.
Speculative fiction, broadly, includes the stories that are typically classified as science fiction and fantasy, but if you've written in the genre realm for long, you may have noticed that the terminology employed by libraries and other sources to classify genre fiction is somewhat limited. Maybe we genre writers aren't as "serious" as the "real" authors, but that hasn't stopped us from developing our own terminology to help describe our works. Since I think that many of these terms would be useful for both readers and writers to know, I've sought to describe some of them below.