Extensive surveillance that is performed by multiple people on a much smaller group or a single individual. It is normally performed by governments who need to keep constant tabs on high profile targets, but can also be carried out by private entities.

Quite often, the people who claim that they are being gang stalked are actually suffering from delusions of persecution and are misinterpreting innocent events as being an attack on them e.g. they will think that a long queue at a supermarket was specifically orchestrated by a large group to make them unhappy.