Multimedia Designing is all about how to design, illustrate, manage, and produce visual communications by software applications, fundamental design principles, web content management, and graphics animation. Multimedia includes a combination of text, audio, still images, animation, video, or interactivity content forms.
Multimedia Design consists of a bunch of different areas of design including graphics, video, web, flash etc. Basically it's pretty much everything to do with design that you can possibly think of Multimedia comes in many different formats. It can be almost anything you can hear or see like text, pictures, music, sound, videos, records, films, animations, and more.