Responsive Web Design

Heard people talk about "Responsive Web Design"... at first had no idea what they are talking about. Isn't all web site supposed to be responsive? Who would design something that is not responsive and just show the hour-glass icon?

Then later I saw some job opening having that as a bullet. Now that makes me look up what this is.

Oh so it is some style techniques so it responds to what type of device you have. After all, a web page nowadays can be seen on various browsers and also tablets and phones and you want to show things differently.

So you need some clever css techniques. Here is that landmark article: http://alistapart.com/article/responsive-web-design

More in depth discussions, for example: http://coding.smashingmagazine.com/2011/01/12/guidelines-for-responsive-web-design/#more-75660

Did you just say "how the heck am I supposed to know?" That's a good question. Usually I focus on coding and let somebody else worry about styles. But I need to have some idea what people are talking about.