What is the difference between a pesticide and an 'Active Substance' (AS) or 'Active Ingredient' (AI)?

The active substance (‘AS’) of a pesticide is the material within the pesticide responsible for its activity against pests, weeds or fungal diseases. AS are sometimes referred to as active ingredients (‘AI’). The plant protection product is the formulated product in its marketed form, which contains that active substance together with other compounds and is applied to the crops.