Final answer:
In property law, a future interest must either become a legal right or transfer to someone else before a person's death plus 21 years. This is known as vesting or failing. A common example is when a person leaves property to one individual for their lifetime and then to another if certain conditions are not met.
Step-by-step explanation:
In the context of future interests in property law, the term "vest" means that the interest becomes a legal right that cannot be taken away. On the other hand, if a future interest "fails," it means that it does not become a legal right and instead goes to someone else. When we talk about an interest vesting or failing by the end of life in being (meaning the life of a person currently alive), it means that the future interest must either become a legal right or transfer to someone else before the current person's death plus 21 years.
Let's say that John owns a piece of land and he wants to leave it to his daughter Mary. However, he wants to ensure that if Mary does not have any children, the land goes to his son Mark. To accomplish this, John includes a condition in his will that states that the land will go to Mary for her lifetime, and if she has no children at her death plus 21 years, it will go to Mark. In this scenario, the future interest of Mark has to either vest (become a legal right) or fail (go to someone else) before Mary's death plus 21 years in order for John’s estate plan to be effective.