A written instrument which authorizes one person to act as another's agent or attorney. The power of attorney may be for a definite, specific act, or it may be general in nature. The terms of the written power of attorney may specify when it will expire. If not, the power of attorney usually expires when the person granting it dies.
This is often used in situations where one is incapacitated, especially mentally. Someone, such as a spouse, would step in with power of attorney over the other's accounts.