Venom, or the Venom Symbiote, is a fictional extraterrestrial life form appearing in books published by Marvel Comics, usually those featuring Spider-Man. The creature is a Symbiote, a sentient alien, with a gooey, almost liquid-like form that requires a host, usually human, to bond with for its survival, as with real world symbiotes, and to whom it endows enhanced powers. When the Venom Symbiote bonds with a human, that new dual-life form refers to itself as Venom.
The Symbiote's first known host was Spider-Man, who eventually separated himself from the creature when he discovered its true nature. The Symbiote went on to merge with other hosts, most notably Eddie Brock, its second and most infamous host, with whom it first became Venom and one of Spider-Man's archenemies.