“Assault weapon” and “assault rifles” are malleable terms often used in public discourse to scare people. After all, all guns are designed to “assault” something. The usual proper use of this term is to describe fully automatic machine-gun-style weapons, which in the United States have been banned from civilian use for years. Notice that the Merriam-Webster change stretches this definition to include anything that looks like such a gun regardless of whether it shoots like one.