So--what the heck is a froehold?

That must be a typo for freehold, which is an estate for life or in fee; the right to a title in land. To be a freehold (can you guess the etymology?), an estate must possess immobility and indeterminate duration.

US property law is still firmly rooted in the soil of feudal England, and the concepts and terminology of those days are still in use.

Seisen was originally the completion of the feudal investiture through possession. Waaaaay back when, the conveyance of real estate was not complete until the granting lord picked up a clump of the dirt and handed it to the grantee.