Microsoft Word: the difference between backgrounds and watermarks?

I'm a bit confused about backgrounds and watermarks in Microsoft Word. Word says taht backgrounds are only for online documents and watermarks are for printed pages. Is there one that can be seen online (like if I email a Word doc) AND if I print it out, or do I have to make 2 separate documents, one with a background, and one with a watermark?

Thanks in advance!

Microsoft Word: the difference between backgrounds and watermarks?new myspace

I don't know... but guess backgrounds are colors while watermarks are pictures. And yep, I made a word document with a watermark and when I saved it as a web page, the watermark wasn't displayed in the web page.