I think these terms are used interchangeably. If a client told me that she wanted a modern look--or used the word contemporary--I'd ask for clarification. But I have the feeling that many people use the word modern when they mean a completely clean, streamlined, almost monochromatic look. Contemporary might be more of an updated look of whatever other style they like. Really though, I think they're just descriptive words. Now, if you said "mid century modern" then you're looking at a defined style!