There is a widely accepted definition for 'assault rifle'. However, 'assault weapon' is vague and controversial. Please don't confuse the two terms.
Also, to the best of my knowledge, this term is almost never used in other English speaking countries. Elsewhere in the world, military small arms are referred to by their accepted names, like submachine gun, assault rifle, crew served weapon, etc. Other small arms are referred to as semi-automatic, double-action, bolt-action, etc. Only in America do we differentiate good guns from bad guns by applying this term to the latter.
If someone outside of the United States has a different understanding, please correct this definition.