Use of vehicle turn indicators (blinkers) at or near roundabouts.

It is, as Juliuss mentioned, it is a measure of the lights turned on in the video, such as the headlights, turn indicators or the back lights.

I think it might be useful to estimate wheather it is day where there are not lights needed or night where the vehicles turn on the lights, but not sure so did not check by hand only based on the description.

It generally represents how actively the vehicle used its turn signals but the exact definition can depend on how the dataset creators defined those categories. eggy car