Bile was a bitter yellow liquid, secreted by the liver, that aided in absorption and digestion.
In 2151, Jonathan Archer told Phlox that Humans used to collect the bile of black bears as an aphrodisiac. (ENT: "Fight or Flight")
In 2365, on the tenth anniversary of Worf's Rite of Ascension, he intoned as part of the ritual: "The bile of the vanquished flows over my hands." (TNG: "The Icarus Factor")
In 2399, Kestra Troi-Riker cut the venom sac out of the meat of a bunnicorn, an animal native to Nepenthe. When her mother, Deanna Troi asked her if she did, she jokingly told her that she left it in so that they could vomit black bile and die. (PIC: "Nepenthe")