To rip a CD means to copy data from the CD to a hard disk or similar destination. The process generally involves changing the original file format to one more suitable for general use and sometimes compressing the data.
The formal name for the process of exacting audio files from a CD is DAE (Digital Audio Extraction), though ripping can refer to the process of obtaining both digital and analogue material. A file which has been obtained in this way can be described as a rip. In comparison, the process of copying, or writing, data to a disk is called burning.