Is there a name for this method of displaying UI Icons on a website? How is it done?

Question

I will take the example of stackoverflow itself:

Stackoverflow displays icons using a single image (see image below):

• What is this method of displaying icons called?
• How is it done?

Answer 1

css sprites

http://css-tricks.com/css-sprites/

basically it uses css to pick which part of the image to display. it saves on round trips for fetching the images.

that link gets into the details on how it works.