A more thorough explanation:

Possession unity refers to the requirement that each joint tenant must be entitled to possession of the whole property. This is one of the four unities required for the creation of a joint tenancy in common law.

For example, if two people own a house as joint tenants, they both have the right to possess and use the entire property. They cannot divide the property into separate parts and claim exclusive possession of one part each.

This unity ensures that joint tenants have equal rights to the property and cannot exclude each other from any part of it. It also means that joint tenants must make decisions about the property together and cannot act unilaterally.