Joint tenancy is when two or more people are on the title of a piece of property together. That piece of property could be real property, it could be a bank account, it could be anything of value.
Joint tenancy assumes that when one person passes away, the survivor or survivors have whatever’s left and continuing on if you have multiple owners. The reason that doesn’t always work is in a lot of cases, people would want their child share to go to their grandchildren if that child died before them. So let’s say a couple of had a son and a daughter, and they want everything 5050 between the son and the daughter, while the daughter passes away, they would want the daughter’s 50% to go to her kids.
However, if you have everything titled joint tenants, that’s not going to happen. Everything in that case is going to go to the son and that daughter side of the family will be effectively disinherited.