Let’s geek a little bit… but don’t worry, it won’t be too freaky! Let’s start with a simple, but important, illustration:

Pixel vs. Vector

Pixel vs. Vector

The Pixel
One of the biggest and most important differences between ON and OFF media is that all screens are based on Pixels and NOT Points. All measurements given will represent this little element (width x height px).
http://en.wikipedia.org/wiki/Pixel

Bitmap
Raster graphics
http://en.wikipedia.org/wiki/Raster_graphics

RGB Color Model
Red – Green – Blue
http://en.wikipedia.org/wiki/RGB_color_model

CMYK Color Model
Cyan – Magenta – Yellow – Black
http://en.wikipedia.org/wiki/CMYK_color_model

RGB CMYK Model

RGB CMYK Model

Web Colors
http://en.wikipedia.org/wiki/Web_colors

True Color
http://en.wikipedia.org/wiki/Truecolor

Color depth
http://en.wikipedia.org/wiki/Color_depth