A person who owns property alone is known as a:

A person who owns property alone is referred to as a tenant in severalty. This term signifies that an individual has sole ownership of the property and holds the title without any co-owners. The concept of severalty emphasizes the exclusivity of ownership, where the owner has complete control over the property and the right to transfer it as they see fit.

The other terms typically imply some form of shared ownership or joint ownership with others. A tenant in common, for example, indicates that multiple individuals own a property together, each holding an undivided interest. Co-ownership involves shared rights and responsibilities among multiple owners, while a tenant by the entireties is specific to married couples, where the property is jointly owned with rights of survivorship. Therefore, "tenant in severalty" is the correct choice for an individual owner with sole control of a property.