What is the definition of DUI in Georgia?

What is the definition of DUI in Georgia? Does it only apply to alcohol or can you also be DUI for smoking marijuana?

Answer:  This question could require a long answer, but to summarize:  It is illegal to drive a vehicle in a less safe manner due to the alcohol you have consumed.  It is illegal to drive a vehicle with an alcohol level above .02 if you are a minor, .04 if you are a truck driver (have a CDL license), and over .08 if you are over 21.  It is illegal to drive in a less safe manner while under the influence of drugs, illegal drugs or prescription drugs and the state is required to show that the drugs consumed caused you to be a less safe driver due to the consumption of those drugs.