A more thorough explanation:

A disposing mind refers to the mental ability that a person must have to prepare a valid will. This capacity is often described as the ability to recognize the natural objects of one's bounty, the nature and extent of one's estate, and the fact that one is making a plan to dispose of the estate after death. Traditionally, the phrase “of legal age and sound mind” refers to the testator's capacity.

For example, if someone wants to create a will, they must have a disposing mind to understand what they are doing and who they want to leave their possessions to after they pass away. If they do not have a disposing mind, their will may not be considered valid.

It is important to note that a disposing mind is just one aspect of capacity, which can also refer to a person's ability to enter into a binding contract or understand the nature and effect of their actions.