Which of the following has an indeterminable duration?

The correct answer is a license, as it has an indeterminable duration. A license is a personal privilege granted to use another person's property in a particular way. Unlike a lease or estate, which can establish defined terms for duration and rights, a license can be revoked at any time by the property owner and does not convey an interest in the property itself. This means the duration of a license is inherently uncertain and can change based on the landowner's wishes.

Freehold estates generally have a potentially indefinite duration, typically lasting until the owner decides to sell or convey the property. Less than freehold estates, often known as leasehold estates, also have a defined duration typically set out in the lease agreement. An estate for years has a clearly defined start and end date specified in the lease terms, making them determinate in their duration.