Web fonts are hosted by an external server or service such as Google Web Fonts, Adobe Typekit, or Monotype Inc. Font.com. These web fonts allow designers to pull typefaces from a server to display those typefaces on thei own websites.
Without WEb Fonts, a user's computer may not display the right font because their computer lacks the proper files. It is very important to declare and use web fonts, or a user's computer will determine a replacement automatically. Sometimes those replacements are embarrassing.
Web Fonts vs. @font-faces
@fonts-face is a CSS feature that allows you to use fonts that exist on your computer as a web font. It is advisible that you only use @font-face when you are certain your typeface has the correct coppyrights that allow it to be used as a web font.
Web Fonts are typefaces that have been optimized and cleared for use on websites.
Pseudo Classes deal with 'events' in CSS. Typically, a pseudo class will wait for the user to perform a certain action before it runs the CSS code.
Pseudo classes are written with selectors, like this...
In the example above, the pseudo class is: hover. This class waits for the user to hover their mouse cursor over an element before the CSS will run.