What does "rock bottom" mean?

The very lowest possible level.

What is a synonym for "rock bottom"?

Common synonyms include: base, basement, basis, bearing wall, bed, bedding.

noun

noun ·Uncommon ·Advanced level

Noun

1
The very lowest possible level. idiomatic, uncountable
"Pork belly futures have hit rock bottom."
2
the absolute bottom wordnet
3
The lowest possible state in one’s life, whether mentally, socially, or otherwise; often, a period of extreme mental stress, homelessness, or rejection by all friends and family. idiomatic, uncountable
"Some people believe that mental illnesses can't be treated unless the person hits rock bottom first."

"Pork belly futures have hit rock bottom."

Derives from the substratum of the seafloor, which is situated below the sand.