Joint Tenancy
You and your spouse buy a house. (Sounds like the start of a Seuss book, doesn't it?) You guys now have joint tenancy for the property. You own it together.
Joint tenancy comes with what's called "right of survivorship," which means that, if one of you dies, the other becomes the sole owner of the entire property.
Joint tenancy differs from other forms of co-ownership, most particularly a situation known as "tenancy in common." Under that form of ownership, you and your partner would own the property together, but wouldn't have right of survivorship. If you die, you could leave your share of the property to someone else. Your co-owner doesn't necessarily become sole owner unless you specifically leave them your portion.