In the Marvel Universe, the symbiote that bonds with Eddie Brock is Venom.
The alien symbiote first encountered Peter Parker during the 1984 Secret Wars storyline, where it became Spider-Man’s black costume. Parker eventually rejected it after discovering its dangerous influence. The abandoned symbiote later found Eddie Brock, a disgraced journalist who blamed Spider-Man for ruining his career. Their shared hatred created Venom.
Venom is more than a costume: the symbiote and Brock form a combined character with their own motives, memories, and abilities. It grants Brock superhuman strength, agility, durability, wall-crawling, shapeshifting, and organic webbing. It can also bypass Spider-Man’s spider-sense because it already knows Peter’s abilities.
A common mix-up is confusing Venom with Carnage or Toxin. Carnage is the offspring of the Venom symbiote bonded to serial killer Cletus Kasady, while Toxin is another later offspring. Brock has also temporarily bonded with other symbiotes, but Venom is the name most specifically associated with his famous partnership.