In weight training the definition of a set, is specific number of repetitions of the same exercise. Give me a set of 10 sit ups, and a set of push ups (implied 10 in that sentence) because the set was defined with the 10 sit ups.
I do not have an answer to the comtemporary term.....
The brain gets used to you taking the drug. Some drugs will affect your neurotransmitters, or messages that get sent to your brain that regulates how we think or feel. You will eventually become dependent on the drug so if you stop you might feel sick or go through "withdrawal". Which people dont want to go through so they will continue to take the drug.