Back in the day (Before e-mail) corporations and celebrities would correspond via traditional mail with a handwritten note. Often times, the note would be on letterhead.
A letterhead is the heading at the top of a sheet of letter paper. It usually consists of a name and an address, and a logo or corporate design, and sometimes a background.
The website Letterheady pays homage to offline correspondence; specifically letters with a focus on the design of the letterhead. Check out their site HERE, some of the examples are fascinating.