What are grid output devices and bitmap output devices for the grid media feature?

What are开发者_如何学JAVA grid output devices and bitmap output devices for the grid media feature?

From the "Internet Encyclopedia":

"Grid media consists of a grid or array of discrete characters. Examples include traditional computer terminals and character printers"

Grid and Bitmap also appear to be supersets of other media types and are counter to each other:

http://www.w3.org/TR/2009/CR-CSS2-20090908/media.html#media-groups

So a "grid" media query would match any of the following:

1. terminal
2. braille device
3. handheld with limited display (perhaps older solution for the visually impaired)