A letter of intent is a document that talks to someone about something you want to do or something you plan to do. It might be a letter you write to someone you want to work with, or to a school you want to attend, or a company you want to buy. It tells the person or company what you are interested in, why you think it is a good idea and how you plan to make it work. You might include details like what you plan to do and how you plan to do it. It's like saying, "Hey, I have an idea and I'm serious about it.'