Assault rifles, by definition, have select fire capabilities. Commercially available civilian AR-15 is semi-auto single fire only. People are often confused by the AR designation, but that stands for Armalite, the original manufacturer of the rifles. They are officially called "assault-style" rifles, although that term isn't very popular because it seems like a minor quibble. In all other measures (shorter rifle, intermediate cartridge, detachable box magazine, range of 300 meters) the AR-15 meets the criteria to be called an "assault rifle," except for the select-fire.

It's worth mentioning that many popular models can be easily modified by a competent gunsmith to add burst and/or full auto firing. It's illegal, but that doesn't stop a terrorist who thinks they are going to need their rifle to join the insurrection. At that point it would be an assault rifle.

Internet comments are crazy. AR15s are semi auto. The first 3 definitions I found would not include an AR15.

https://en.wikipedia.org/wiki/Assault_rifle

https://www.britannica.com/technology/assault-rifle

https://www.merriam-webster.com/dictionary/assault%20rifle - this second definition includes semi auto rifles however

The AR-15 defined assault rifles in a way. Outside of experimental weapons. Most countries that use assault rifles are based on the AR-15, the cheaper to licence AR-18 or the Soviet response to the American AR-15/M16.