Lane departure assist can refer to one of two systems:
A Lane Departure Warning (LDW) system can warn the driver of an unexpected lane departure through an audible or visual warning.
Sometimes it can also include a vibration in the seat in the direction of the threat (for example, if the car is drifting towards the left side of the lane then the left side of the seat will vibrate to alert you).
A Lane Keep(ing) Assist (LKA) system takes the above to the next level by actively keeping your car inside the lane if it detects that you are about to leave the lane unexpectedly.
Some systems will only take action if the car starts to drift towards the outside of the lane, while other systems actively work to keep the car centred in the lane at all times.
Things to be aware of: