A power of attorney is the means you use to have your affairs managed should you become unable to manage your own affairs. There are a couple of situations where somebody would become unable to manage their own affairs such as when a person loses or temporarily loses mental capacity, or when somebody has gone into a comma. In these situations may be desirable or even necessary for somebody else designated by you to carry on your personal affairs. This is achieved with a power of attorney. There is more than one kind of power of attorney such as a springing power of attorney or a durable power of attorney.
Each of these variations has its benefits and drawbacks. For example certain types require that the principal be found incompetent. This sounds simple enough but can often be a rather large hurdle and can consume valuable time.