I consider “assault weapon” to be redundant. I also consider “defensive weapon” not to be an operational description, but a promise of restricted use that is not built into the weapon. Any weapon in operation, from fist to aircraft carrier to software weapons, projects power i. e. assails.
(Edit: I wondered about mines, since their operation is automated. I decided that, since they project damaging energy, they satisfy the definition of a weapon. Punji sticks are more problematic. I’m inclined to class them as fortification of the same sort as an electrified fence.)
Entirely defensive hardware falls imo into the domain of armor and fortification. Reactive armor is an interesting if narrow gray zone.
Sensor tech can also be defensive, though it is usually paired with a weapon in a weapon system, with the above reservation applying.
Less formally, an assault weapon is a firearm, typically a semiautomatic rifle or carbine, styled after (but generally not qualifying as) an assault rifle/carbine. I find it to be more of a subjective term, often used to recruit voter sentiment.