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 Design programs can help accomplish the look / feel that you are going for. For example, Flash is a multimedia program that allows for basic animation. You don't necessarily have to be a programmer to use it, but having that knowledge does allow you to do more with the program. Multimedia Icons

A blog is sometimes referred to as an online personal journal. It is a site designated for an individual to write about his/her daily experiences, to illicit thoughts and often allowing readers to offer their comments. The term is a shortened form of “weblog”. Authoring a blog, maintaining a blog or adding content to an existing blog is referred to as "blogging". Individual articles on a blog are referred to as “blog posts”, “posts”, or “entries”, and the person who created the blog post is often called a “blogger ”.

 Multimedia could be anything that has to do with the internet, blogging or webs.  Interactive Media is such as text, graphics, animation, video, audio, games, etc.  A podcast is a multimedia digital file made available on the Internet for downloading to a portable media player, computer, etc.