Venom, or the Venom Symbiote, is a symbiote life form created for the Marvel Comics universe. The creature is a sentient alien with a gooey, mercurial like form. It requires a host, to bond around for its survival. In return the Venom creature gives its host enhanced powers. In effect, when the Venom Symbiote bonds with a human to form a super-villain, that new dual-life form itself is also often called Venom. The symbiote, with or without a host, is one of Spider-Man's archenemies. Spider-Man was the first host it merged with before its evil motives were clear. After Spider-Man rejected it, the symbiote went on to merge with other hosts and so began its popular reign as the villain known as Venom.

I figure y'all know who batman and spidey already are.