A more thorough explanation:

Definition: Casu proviso is a Latin term that means "in the case provided." It refers to a writ of entry used to recover a reversion in land that was sold or given away by a tenant in dower. A tenant in dower is a widow who has a life estate in the land.

Example: Let's say that John owns a piece of land, but he dies and leaves it to his wife, Mary. Mary has a life estate in the land, which means she can use it and enjoy it during her lifetime. However, she cannot sell or give away the land because it will eventually go back to John's heirs. If Mary does sell or give away the land, John's heirs can use a casu proviso writ of entry to recover the land.

Explanation: This example illustrates how a casu proviso writ of entry can be used to recover land that was sold or given away by a tenant in dower. In this case, Mary was the tenant in dower, and she sold or gave away the land, which was not allowed. John's heirs can use the writ of entry to recover the land and ensure that it stays in the family.