Summary: In ABA, punishment has a technical meaning that has nothing to do with anger or harshness. A consequence is punishment only if it makes the behavior happen less in the future. This page covers positive and negative punishment, the two procedures you'll most often implement under a plan (time-out and response cost), and the rules that surround all of it: reinforcement comes first, least restrictive wins, and you only run what your BCBA designed and the family consented to.
Let's clear up the biggest misunderstanding in this whole topic before we go anywhere. The word "punishment" in behavior analysis does not mean what it means at the dinner table. It isn't about being stern, it isn't about consequences feeling bad, and it definitely isn't about making a kid sorry. Punishment is defined by one thing and one thing only: did the behavior go down afterward?
If a consequence follows a behavior and the behavior decreases in the future, that consequence functioned as punishment. If the behavior didn't decrease, then whatever you did, it wasn't punishment, no matter how unpleasant it looked. That's the part the exam hammers, and it's the part new RBTs get wrong over and over.
As an RBT you'll rarely, if ever, be the one deciding to use a punishment procedure. Your BCBA designs the plan. But you need to understand these procedures cold, because you may be asked to implement the gentler end of them (a time-out, a response cost), and because the exam will test whether you can tell punishment from reinforcement and positive from negative without flinching.
Punishment is defined by its effect, not by being aversive
Here's the rule, stated as plainly as I can: a consequence is punishment if, and only if, the behavior it follows decreases in the future.
That's the free preview of Punishment Procedures. The complete guide, plus all 851 practice questions and 3 full exams, is in the study pack and the book.