A more thorough explanation:

Mortmain

Mortmain is a French term that means "dead hand." It refers to land or property that is held by a church or corporation and cannot be sold or transferred. This is because the corporation or church does not die, so the property remains in their possession indefinitely. In the past, this was called amortization. However, this practice was seen as unfair and against public policy, so the Rule Against Perpetuities was created to prevent it.

An example of mortmain would be a church owning a piece of land that they use for their services. This land cannot be sold or transferred to anyone else because it is held by the church in perpetuity. Another example would be a corporation owning a building that they use for their business. This building cannot be sold or transferred because it is held by the corporation in perpetuity.

These examples illustrate the definition of mortmain because they show how land or property can be held by a church or corporation and cannot be sold or transferred. This is because the church or corporation does not die, so the property remains in their possession indefinitely. This practice was seen as unfair and against public policy, so the Rule Against Perpetuities was created to prevent it.