Aim Assist vs. Auto-Aim.

...again.

Aim Assist can be used as a generic term, but more often refers specifically to Passive Aim Assist. Active Aim Assist like DUST has is better known as Auto-Aim.

Passive Aim Assist is when your turn speed is dialed up slightly when turning towards a target, and slows down when turning away. This means that "wiggling" the stick will gradually centre your aim on a target, but it doesn't move the crosshairs without player input.

Active Aim Assist is what DUST has, which most competent players turn off anyway. This actually follows targets - though not accurately in DUST, and not very fast - when they move.

Passive Aim Assist - which is what should be called aim assist - exists in almost every console shooter ever made, and it's a very good thing to have in a console shooter, because it helps to compensate for the lack of precision inherent with the standard controls. Auto-aim is generally seen as a negative for competitive play, and is almost always turned off by competent players because it actually throws your aim off when you're good at aiming for yourself.