coaster

n. 1. Unuseable CD-ROM produced during failed attempt at writing to writeable
or re-writeable CD media. Certainly related to the coaster-like shape of a CD,
and the relative value of these failures. I made a lot of coasters before I
got a good CD. 2. Useless CDs received as junk snailmail in the 1990s from the
likes of AOL, MSN, CI$, Compuserve, Prodigy, ad nauseam. In the U.K., beermat
is often used in these senses.