Halāhala (Sanskrit हलाहल) or kālakūṭa (Sanskrit कालकूटं, literally: 'black mass' or 'time puzzle' ) is the name of a poison (as per Hindu mythology) created from the sea when Devas (Gods) and Asuras (Demons) churned it (see Samudra manthan) in order to obtain Amrita, the nectar of immortality.
Fourteen different rathnas (gems) were recovered in this exercise, mostly retained by the Gods after the Demons tried to cheat them. But before Amrita could be recovered, Halāhala ("the most vicious and venomous poison of universe") was produced, which started killing both sides. As no one could bear the poisonous fumes emitted by the poison, both Devas and Asuras began to collapse due to asphyxiation. They ran for help to Brahma, who directed them to Vishnu who advised them only Shiva could help them. So both parties went to Kailasha and prayed to Lord Shiva for help. Shiva chose to consume the poison and thus drank it. His wife Parvati, alarmed, stopped it in his throat with her hands, thus earning him the name Viṣakaṇṭha (the one who held poison in his throat). He was later saved by the mahavidya (tara) who is also a form of parvati. The poison made his throat turn blue; hence, he is also known as Nīlakaṇṭha (the one with a blue throat).
There is a proverb in Hindi language, derived from this incident: Amrit paane se pahle Vish peena padta hai. Literally meaning: before one can get Amrit, one must drink poison. Used generally to imply: Before one becomes successful, one will face many odds in life.