Adobe InDesign is a desktop publishing (DTP) software application produced by Adobe Systems. It can be used to create things such as posters, flyers, brochures, magazines and books.
InDesign is a direct competitor to QuarkXPress.
Indesign is a page layout program. So basically, you take text and pictures and you put them all together to make files like postcards, brochures, flyers, business cards, etc. This way you have less lag on your computer memory and better features for proffessional printing, and heck its easy to use at home too.