What does cover letter mean?

Covering letter is a kind of attachment with the written document being sent that specifies the details with regard to the information being sent as well as serve as the outline or layout of the writen document.

-------------------------------------

A letter sent along with other documents to provide additional information
My basic understanding of a cover letter was that it was basically a cover for a paper or report or resume. It's the first page that the person going to look at this stack of papers will see and generally (more likely if it's a resume) determines whether or not someone will still want to read what you gave them.