What is a RIP?
RIP stands for Raster Image Processor. It's basically a translator between your computer and printer, that translates the code your computer spits out (PostScript) into code that the printer understands (bitmap).
Your printer driver (such as AdobePS) is a kind of RIP that does some translation right on your computer before it goes to the printer (that is, translating the code from your DTP program into PostScript code). Most desktop printers have built-in RIPs (such as PostScript 3) that handle the more complicated stuff.
Bigger, more complex (and much more expensive) printers often come with separate RIPs (if you've ever seen something that looks like a computer tower connected to a big printer, chances are it's a RIP). These RIPs tend to have more features (such as queue handling, colour-matching, ink density alterations, etc.).
Huge press machines tend to have the most complex RIPs (now we're talking really expensive), and to be honest, I don't know that much about them: Press operators tend to foam at the mouth and shoot anyone who comes close to their RIPs and presses.
Follow the link below for a more detailed article on RIPs
Reference: About.com
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