What nickname did Metallica's nearly black cover give the 1991 album its popular name?

Metallica's nearly black cover gave the 1991 album the popular nickname The Black Album.

The official title is Metallica, an eponymous name chosen after the band considered several alternatives. The cover places the band's logo in the upper-left corner and a coiled snake, derived from the Gadsden flag, in the lower-right corner.

On the initial release, both emblems were embossed and intentionally difficult to see against the black background. That understated design made the unofficial nickname natural and quickly established it among fans, journalists, and record retailers.

The snake also connects the packaging to the song “Don't Tread on Me,” whose title echoes the motto associated with the Gadsden flag. The nickname is therefore about the visual presentation, not the album's formal title or musical genre.