An ingested poison is a type of poison. Ingested poisons are consumables generally given to other characters through subterfuge and trickery (or just when they are helpless). It should be noted that ingested poisons only give the poisoned condition if they cause a poison call or otherwise specifically say they do. Even if they do not give the poisoned condition a character with an immunity to poison is still immune to ingested poisons.
To use an ingested poison it must be role-played being poured into a drink or onto food (assuming you can't somehow trick someone into drinking the poison straight out of the vial), then a green dot is applied to the container, typically on the bottom. This green dot gives characters with the herbalist skill a chance to identify that the food or drink is not safe before anyone ingests it. In the event that someone ingests the poison they should then be notified of exactly which poison they consumed.
Blade poisons, ingested poisons, and thrown poisons all require the herbalist skill to use. If a character attempts to use any of these types of alchemy compounds they fail to use the item successfully and suffer the effects as if the item were used on them.