hydroponics is a way of growing where the roots sit in an inert medium and either sit in nutrient solution, or have nutrient solution pumped to them as they need it. when growing in soil, the roots sit in the soil which already has some nutrients in it, and water is absorbed by the soil and then by the plant. in hydroponics, the plant sits in a medium (like rockwool or hydroton) which has no nutrients of its own, and nutrient solution is pumped to it at different times. when growing hydro the plant absorbs the nutrients quicker and grows faster.