One who thoroughly enjoys the mary jane. Perhaps they have been accused of loving weed more than their significant other. They smoke when they wake up, before work, during work, if possible, and as soon as they get home. They never run out of weed because they are always planning ahead.
In short, a professional weed smoker.
If you just looked up stoner/pothead on urbandictionary.com while smoking, then you are a pothead.