What type of estate is characterized by lasting for an indeterminable period of time?

A freehold estate is indeed characterized by lasting for an indeterminable period of time, which distinguishes it from leasehold estates and other types of tenancies. This type of estate provides the owner with a significant degree of ownership and is not limited by a specific term or duration as leases are.

Freehold estates come with the rights to possess, use, and transfer the property, and they can last for a lifetime or may even pass on to heirs, thus having a potential indefinite duration. This is in contrast to leasehold estates, which are created for a fixed period and often have specified terms for rent or use. Similarly, a tenancy at will is a more flexible arrangement that can be terminated at any time by either party and typically does not have the permanence implied in a freehold estate. A life estate is indeed tied to the lifespan of an individual and, once that individual passes away, the estate terminates, resulting in a non-permanent holding which does not compare to the uninterrupted duration of a freehold estate. Thus, a freehold estate is the correct classification for an interest that lasts for an indeterminate period.