a "rip" is defined as an alternate copy or rip-off of an original manufactured item. When CD-ROM's first came out, people use to rip-off CD games to fit them onto 3.5" floppy disks.
In PS2, original manufactured DVD games are ripped-off and altered to fit on a 80 min CD-R. (much like Dreamcast). This is done by compressing the video files, the audio (much like mp3 which is 10:1 compression) while still being able to run the game. Some items are cut from the game, others are compressed. Some games however are so big (4.5 Gigs DVD) that they require multiple CD-R disks. This is done by, for example, putting levels 1 to 5 on disk 1, and levels 6 to 10 on disk 2.