Historically ownership was proved by a bundle of paper deeds. Most mature markets have moved to a central register: in England & Wales HM Land Registry's title — identified by a unique title number — is conclusive as to the registered proprietor, the tenure (freehold/leasehold), charges (mortgages) and any restrictions or notices.
In Dubai the DLD issues an electronic title deed (and an Oqood registration for off-plan) confirming the owner, plot, and whether the tenure is freehold or leasehold. In the US title is evidenced through the county recorder's chain of deeds, which is why title insurance exists to cover defects in that chain.
Before you buy, the title is read for three things: that the seller is the registered owner, what rights and burdens run with the land (easements, covenants, leases), and what charges must be discharged on completion.