Poison-type is one of 18 type classifications that is assigned to type-moves and Pokemon who's physiology are closely associated with that of venom or sometimes toxic waste. These types are most often dual-typed with others, with pure Poison-types being quite small in comparison. As a result, Poison-typed Pokemon can be found in just about any location.
Defensively, Poison-typed Pokemon are resistant against Fairy-, Grass-, Fighting-, Bug-, and other Poison-type moves; though are weak against Ground- and Psychic-typed attacks. Offensively, Poison-type moves are effective against Fairy- and Grass-typed Pokemon, while lacking in effectiveness against Ground-, Rock-, Ghost- and other Posion-typed Pokemon, and are further ineffective against Steel-type Pokemon.
Poison-type Pokemon enjoy an immunity to poisoning effects, with the exception being Pokemon with the Corrosion ability. Furthermore, grounded Poison-types will remove Toxic Spikes that are deployed against their side when they enter battle.