WordPress shortcodes are small lines of code which you add to any blog post or page. These are WordPress-specific code that let you do nifty things with very little effort. Shortcodes can embed files or create objects that would normally require lots of complicated code – in just one line. So shortcodes are shortcuts in wordpress.
As an example, The WPSalesGraphic Plugin gives you the ability to create professional Sales Box, Buy Now or Video Optin graphics that you can add to any page with a simple shortcode that you type into your post. You simple type in something like “[salesboxe id=1]” and the plugin knows that this represents a specific type of graphic.