Just do an internet search of "assault rifle." You'll find there is not one definition. It is also possible, although illegal, to convert an AR-15 to full automatic mode (another internet search will tell you this).

According to the first response I found, and AR-15 is an assault riflge. YMMV

https://www.wordnik.com/words/assault%20rifle

In general from reading, the major difference is a high capacity magazine and barrel length. A longer barrel makes for a better hunting rifle. AR-15s usually have barrels shorter than hunting rifles, making them eaiser to handle in a fight, and because assault targets are not so far away as deer in the forest.

The magazine capcity is obvious. 1-3 shots is enough for hunting. An AR-15 magazine holds 30+ rounds. Clearly that is not needed for hunting...deer.