An easement is a right to use another's land but without the right to possess or enjoy the land. Presumed to be of perpetual duration.
Affirmative v. Negative
Most are affirmative (right to make use of another's land). Negative easements (which compel possessor of servient tenement to refrain) are only for: light, air, lateral and subjacent support and flow of artificial stream.
Benefits easement holder in his physical use/enjoyment of another's land. Need 2 tracts: the dominant and the subservient. Benefit passes with dominant land -- regardless of mention in conveyance. Burden also passes with subservient land, unless BFP without notice.
Easement in Gross
Right to use servient tenement without possessing land. Example: PG&E has easement in gross to install utility poles. Transferrable if for economic use, not if for personal use.
Easements - Creation
Easements - Termination