Which is dictionary definition(below link) of "Schedule" used in the website above link? http://www.learnersdictionary.com/definition/schedule
Drug scheduling is a way of ranking illegal drugs based on their medical value and potential for abuse. Countries use scheduling systems to determine how to enforce laws against certain substances. The scheduling system usually ranks in numbers, and different countries have their own classifications for each drug, albeit mostly similar to each other and the United Nations (UN).
The UN classifies drugs from Schedule I through IV, using the same concept of medical value and potential for abuse, albeit worded differently.