Which of these best describes an estate at will?

An estate at will is characterized by its indefinite duration until one party decides to terminate the agreement. This type of tenancy is often established when a tenant occupies property with the permission of the landlord, but without a formal lease agreement specifying a definite period. Because there is no fixed term, either the landlord or the tenant can terminate the tenancy at any time, adhering to any required notice periods as stipulated by local laws.

In contrast, a fixed duration tenancy would have a clearly defined end date, which does not apply to an estate at will. A monthly rental agreement typically indicates a periodic tenancy, where renewals and obligations are formalized each month, which is not the essence of an estate at will. Tenancy requiring administration approval usually refers to more complex arrangements that necessitate additional oversight or consent, rather than the simplicity of an estate at will.