What is a letter of instruction?

A letter of instruction is a very important document frequently, in estate planning and Elder law my clients will execute a letter it's informal; it's not a legal document but it accurately expresses their intention on what they want the personal representative to do upon their death or what they would like their healthcare surrogate to do or what they would like their guardian to do. I find it's very helpful my clients can put it in their own terms and it's not public.