They are often called "side lights" but, strictly speaking, they are "parking lights". In the U.K. between sunset and sunrise all motor vehicles parked on a road must be parked with the nearside of the vehicle as near to the kerb as possible and the vehicle cannot be parked within 10m of a junction without any lights on.
There are exceptions,
Parking within 10 metres of a junction with lights on
Parking on a one way street
Vehicles dropping off or picking up passengers
Vehicles connected with emergency services
Vehicles connected with building work, repairs to road, cars, sewers, gas pipes etc.
If the road does not have a 30mph limit then parking lights must be used when parking a vehicle in the hours of darkness.
A heavy goods vehicle (over 7.5 tonnes) must be lit and must not cause an obstruction if parked on a road during the hours of darkness.
A failure to comply with these rules will lead to a fixed penalty notice being issued. That being said, I do believe (a) drivers do not know the law anymore and (b) nor do the Police otherwise they could have a field day and be issuing 000's tickets a night
Jeff