To record all the data on a CD-R disc at one time. The lead-in (table of contents), all the tracks and lead-out are written, the session is finalized, and the disc is closed. The laser is kept on for the entire session, and the two-second gaps between tracks are eliminated. At one time, CD manufacturers asked for disc-at-once CD-R masters to ensure a proper reproduction, but this requirement has been mostly relaxed. See track-at-once.