A special permission to do something on, or with, somebody else’s property which, were it not for the license, could be legally prevented or give rise to legal action in tort or trespass.
A common example is allowing a person to walk across your lawn which, if it were not for the license, would constitute trespass.
Access to a shopping mall is on the basis of an implied license.
Licenses are revocable at will (unless supported by a contract) and, as such, differs from an easement (the latter conveying a legal interest in the land).
Licenses which are not based on a contract and which are fully revocable are called "simple" or "bare" licenses.