What is an easement in gross?

Unlike easements appurtenant, which provide a benefit to all possessors of a parcel of land, an easement in gross is an easement that is given to a specific person. For example, imagine that Bob owns a parcel of land with a boat dock on a lake. An easement appurtenant would be an easement that provides all possessors of a specific, neighboring piece of land the right to access Bob's dock. An easement in gross is an easement that allows a specific person (who doesn't own a parcel that touches Bob's land) the same right.

Imagine if Amy and Bob both owned parcels of land next to each other, next to a lake. Amy's parcel has a bunch of rocks on its shore making it difficult to build a dock for her boat. Bob already has a dock. Bob hates Amy, so he explicitly tells her to never use his dock and never trespass on his land. Dan, a friend of Bob's who lives 15 minutes away, recently bought a boat. Bob gives Dan an easement allowing him to make use of his dock when he's in town. Dan has received an easement in gross. It is an easement that specifically attaches to Dan and no one else.

Note that if Dan made use of the easement commercially (if he was a fisherman, for example), the law would allow him to transfer the easement in gross if he, for example, sold his business to someone else.