AR-15-platform rifles are among the most popular firearms being sold. They are today's modern sporting rifle.
The AR in "AR-15" rifle stands for ArmaLite rifle, after the company that developed it in the 1950s. "AR" does NOT stand for "assault rifle" or "automatic rifle."
AR-15-style rifles are NOT "assault weapons" or "assault rifles." An assault rifle is fully automatic -- a machine gun. Automatic firearms have been severely restricted from civilian ownership since 1934.
AR-15-style rifles look like military rifles, such as the M-16, but function like other semi-automatic civilian sporting firearms, firing only one round with each pull of the trigger.