Joint tenancy with rights of survivorship is when individuals own equal shares in a property. Often, spouses hold property as joint tenants. All joint tenants must agree to a sale, to protect spouses from having their property sold without their knowledge. If a joint tenant dies, the other joint tenant inherits their share in the property. The survivor "wins" and takes sole title, no probate required. It does not matter what any will says.
There is also tenancy in common, which allows people or commercial partners to own equal or unequal shares in a property. It is also used by married couples who want to trigger an estate at each spouse's death for estate planning purposes.
These types of ownership can become complicated, and the advice of a competent real estate attorney can be helpful to a real estate buyer.