banner impression

Tweet

What is a banner IMPRESSION? Is it the same thing as a regular old banner only with a better name? I have seen the term in a lot of places and I never paid any attention to what exactly it was. And now I belong to a site that offers banner impressions to its users and I have 5 available and now i need to know what the impression part means. Obviously I know what a banner is. Just need to know whether or not the impression part is important and if it is, what it is!