Sleep Dirt is an album by Frank Zappa released in January, 1979 on his own DiscReet Records label. It reached 175 on the Billboard Pop Albums chart. Zappa's intended title for the album was Hot Rats III. The title was changed by DiscReet's distributor, Warner Bros. Records in violation of Zappa's contract.
Zappa had originally envisioned three of the album's tracks ("Flambay", "Spider of Destiny", and "Time Is Money") being used in his (abandoned) Hunchentoot musical, and thus, these songs were intended to have vocals. For the CD reissue of Sleep Dirt, Thana Harris overdubbed vocals on the aforementioned tracks, and Chad Wackerman overdubbed drums. The original, instrumental versions of these tracks can be found on Läther (though "Flambay" was greatly shortened; the full-length instrumental version of that can only be found on the original LP.)
The creature shown on the cover is Hedorah from the Godzilla films.