What is freehold?
Freehold means you own the property and the land it stands on outright, for an unlimited period. There is no landlord, no ground rent, and no lease term running down. Most houses in England and Wales are freehold.
Ownership is not unconditional. Restrictive covenants can limit what you do with the land, rights of way can cross it, and rentcharges still exist on some estates. These appear on the register, which is why reading it is worth the few minutes it takes.
New-build houses sold as leasehold were a notable scandal, and the ability of leaseholders to acquire the freehold has been a running policy issue.
Freehold flats are rare and generally unmortgageable, because there is no mechanism to enforce obligations between flats. Commonhold was designed to solve this and is the direction of government reform.