Delineation is the act of representing something or describing it. The portrait you paint of your best friend is a delineation of that person.
A delineation can refer to any kind of pictorial representation of something else, like a geometric sketch or a map of a city. A delineation more generally means any kind of accurate or vivid portrayal of something else. So, a lively summary of a book that makes the listener feel she read it herself can be a delineation. Telling someone else what you dreamed about last night is a delineation of that dream.