What is the defining characteristic of an estate at will?

An estate at will is defined by its lack of a specified duration for the tenancy, meaning that it continues until either the landlord or tenant decides to terminate it. This arrangement allows either party to end the tenancy at any time, but typically requires notice from the party wishing to terminate. The flexibility of this type of estate makes it distinct, as it does not bind either party to a fixed term or require an automatic renewal.

The other options highlight features that do not align with the nature of an estate at will. For example, a fixed-term lease entails a specific duration for the rental period, while a renewal option indicates an agreement to extend a lease under certain conditions. Lastly, a lease that never expires suggests perpetual occupancy, which contradicts the core principle of an estate at will that empowers parties with the authority to terminate the agreement freely.