The terms poison and venom are often used interchangeably, but they actually have very different meanings. It is the delivery method that distinguishes one from the other.
Poison is absorbed or ingested; a poisonous animal can only deliver toxic chemicals if another animal touches or eats it. Venom, on the other hand, is always injected. Every venomous animal has a mechanism (e.g., stingers, fangs, etc.) to inject toxins directly into another animal. It is for these reasons that frogs can be poisonous to touch or eat, while snakes are venomous when they use their fangs to bite.