What is RIP software?
RIP is an acronym for Raster Image Processor. A "raster" is a set of horizontal lines composed of individual pixels, used to form an image. Any digital image (TIFF, JPEG, etc.) will have a raster of pixels. For photographic output, a RIP is any device, hardware or software, that processes rows of pixels from source to output device (printer, computer screen, billboard vinyl, etc.).
A RIP can process data for many different kinds of output: halftone dots on plates or film for lithographic printing, or ink droplets for inkjet printing. A RIP nowadays is usually software-based like ImagePrint, ColorBurst or Qimage. Back in the day, companies such as Linotype made hardware RIPs with proprietary hardware & software, but became outmoded as computer processing power became accessible to the masses.
A RIP for an inkjet printer is designed in a manner that allows the user to output images without ever using the standard printer driver that comes with the printer. To design a RIP like this requires an high level of knowledge in how each model of printer makes an ink dot, how accurately it is placed on the substrate, how the head moves, how the paper advances, and many other aspects of the hardware. The RIP must control all aspects of the printer for it to provide better output than if one were to simply use the standard printer driver.