An easement is a right to use the land of another for the purpose set forth in the document that created the easement.
An easement holder does not have the same rights as an owner [fee interest] such as the ability to transfer the right to others.
Most easements run with the land – even if they are not specified in later deeds, the right is still there. The parcel that benefits from the right is called the dominant tenement and the property which the easement burdens is called the servient tenement.
By their nature, easements are non-exclusive rights, which means that the land-owner can grant the same rights to others and can use the property himself. The only thing that the servient cannot do is prevent the use of the easement.