Taking another business' social media location and promoting another.
Using social media location services (Foursquare, Gowalla, Whrrl, etc) to market a service, product, or brand at a location other than where said item is located.
Used to promote at offsite locations. Also could be used to mock event or business.
Checking into 'Foursquare' at a music festival. Of the places to check in the options could be for said "music festival" and "Joe's Burger across the street". Those checking in would see both items. It would be a free ad for Joe's Burger for those that check in because of "location jacking".
To mock or degrade one could make up a location called "rip-off festival" or "waste of money fest".