Ripping, more formally known as digital extraction, is the process of copying audio or video content from a compact disc, DVD or streaming media onto a computer hard drive. A ripper program has an encoder to compress the source media and reduce the size of the file it stores on the hard disk. It may also have a converter program to allow the user to change the media's file format. The process of re-copying the converted files to a recordable CD or DVD is called burning.
Despite its name, ripping programs have nothing to do with the slang phrase "rip off," which means "stealing." There are various explanations as to the derivation of the term. According to one common theory, the programs are called rippers because the digital copying process can be very fast -- especially when compared to the time it would take to re-record sound or video from the source output. However, the term may actually derived from raster image processing (RIPping):
I actually heard the term "ripping" many years (20?) ago specifically applied to the conversion of analog video to digital format; at the time, I actually understood it as being derived from the acronym RIP: Raster Image Processor. I.e., it referred to what a physical piece of hardware did: rasterizing a stream of analog video frames. I'm guessing that it then got a bit more generic, covering analog-to-digital conversion of other media, in particular vinyl and tape audio. Small step, then, to the current meaning: capturing any media and converting it to another format (nowadays mostly digital-to-digital).
~ Ulf Olsson, Ericsson Sweden
In most countries it is perfectly legal for someone to make a copy of commercial audio media he owns for personal use as long as he does not share the copy with anyone else or distribute it commercially. In the United States, the Motion Picture Association of America is against the idea of extending that same policy to commercial video.
Mark Harris provides a tutorial for using Windows Media Player to rip CDs.
The Recording Industry Association of America (RIAA) provides guidelines for legally copying music.