Since there is no accepted definition, it is an honest question as to how you would define it. I would say rifles with detachable magazines is the only principled way to define it.
Often, people pushing a ban on "assault weapons" are seeking to ban automatic rifles, and are then shocked to find out that they are already effectively banned. Yes, there are some out there, but they are owned by people with special licenses, who get inspected, etc. It's a big deal to own one, and they are not involved in crimes as a general rule. There may have been one or two in the past 60 years.