It's roughly knife-shaped, but often with a wooden handle. The tip is rounded and the edges are not sharp.
I'll call it a spatula, but usually there's enough context to know I don't mean one of those broad plastic things for scraping the sides of a bowl nor one of those broad things for flipping burgers.
Edit: This question was prompted by this comment on an NSQ post, which used the term “sandwich spreader”. I had never seen that before, but I’m glad that others here also use it (so the author of that comment isn’t crazy) as well as others here using “spatula” (so I’m not crazy. At least not in that regard.)