When an owner dies without a will, the land passes to the heirs the state's intestacy statute names, and they hold it as tenants in common. Each owns an undivided interest: a fraction of the whole property, not a particular room or acre. Nothing is recorded to show this. The deed in the county records still names the person who died, and the title stays tangled until someone proves the heirs and records that proof.
The trouble compounds. When an heir dies, that heir's fraction splits among their own heirs, so four children become a dozen grandchildren with shares like 1/12 and 1/8. Any one of them can sell a fraction to a stranger, and any co-owner, including that stranger, can ask a court to partition the land.
The uniform partition act gives the term a precise test. Texas Property Code Section 23A.002(5) and Florida Section 64.202(6) define heirs property as real property held in tenancy in common, with no agreement in a record binding all the cotenants that governs partition, where at least one cotenant got title from a relative and 20 percent or more of the interests, or of the cotenants, are relatives or came from a relative. California's version skips the test and covers every tenancy in common without a binding agreement (CCP Section 874.311(b)).