Dro is slang for hydroponically grown Cannabis. Hydroponics is a method of growing indoor crops, where the plant are placed in a non soil medium, usually rockwool, Clay Pellets, or Coconut Fibre, and irrigated with fertilized water. The light, humidity, and temperature can be regulated for optimum growth. Despite common misconceptions, Cannabis grown hydroponically will not necescarrily be more potent, or "pure". It all depends on the plants nutrition, and what type of nutrients are used, and in fact, cannabis grown in soil is said to have better a taste. Potency also has much to do with genetics, light spectrum differences, Altirude and a variety of things. The main benefit to Hydroponics is that if growing indoors, more plants can be fit into a smaller space. Hydroponic weed is often grown with sythetic fertilizers, which are often harsh, and toxic if left in the plant (not flushed).