Here's a video from the folks at the Atlantic that heroically attempts to define what is a sandwich: Although somewhat arbitrary, its authors point out that whether or not something is a "sandwich" can be an important distinction, influencing how maybe-sandwiches are taxed and regulated. Under the current system, which could consider everything from burritos to hot dogs to ramen burgers a sandwich, the Atlantic decrees: "it's chaos."
Based on the new definition, hamburgers, pitas, and ice cream sandwiches are considered tried-and-true "sandwiches." Hot dogs and burritos fall into the "not a sandwich" category. Go, watch to discover why: