The term "Dirty Dozen list" refers to yearly list released by the Environmental Working Group indicating the top 12 pesticide laden fruits and vegetables. The list is based off testing done for pesticide residue on produce by the USDA.
The EWG also releases a yearly list known as "The Clean Fifteen." This list comprises the top 15 fruits and vegetables with the least amount of pesticide residue. It is recommended that organic produce is purchased when shopping for items from the dirty dozen list. It is generally regarded as safe to purchase conventional produce when shopping for items from the clean fifteen list.