Assault rifle does not have a definition. It arises out of confusion that the “ar” in ar15 stands for “assault rifle” rather than Armalite. It’s just stupid. The term does not have a definitive definition.
Assault rifles use a medium cartridge and are capable of select fire.
The STG44 was the first of the type.
The AK-47 and the M-16 followed.
The semi-auto only variants are not assault rifles.
They are not capable of select fire.
Illegal aliens are not undocumented immigrants, either.
Could you be thinking of assault weapon? I believe assault rifle does have a definition in the military as a selective fire rifle of medium power. In contrast, assault weapon is some sort of made up political term.