A refers to an effort to preserve disc-based media (and some other formats) by creating 1:1 accurate backups. Unlike a standard "rip" (which may ignore error sectors, copy protection, or unused data), a Redump aims to be a bit-perfect copy of the original master disc.
If you want to backup your own physical discs to Redump standards, standard ripping software (like ImgBurn) is often insufficient because it "corrects" errors by default. redump