An Institutional Review Board (IRB) is a special group of people that makes sure that any research done with people or animals is safe and ethical. It's like a team of grown-ups who check to make sure that researchers are not hurting anyone or doing anything they shouldn't.
When a scientist wants to do an experiment or a study with people or animals, they have to write down what they want to do and why they need to do it. The IRB looks at this and decides whether it's okay or not by asking questions like "Is it safe?", "Will the participants enjoy it?", "Will it cause them harm?", etc.
If the IRB gives the green light, then the researcher can start the study. But the IRB doesn't go away after that. They keep checking in to make sure that everyone involved is okay and happy with what's going on. If they find something wrong or if someone complains, they will fix it to make sure everyone is safe.
Overall, the IRB helps make sure that research is done responsibly and ethically, and that everyone involved - researchers, participants, and animals - are treated fairly and kindly.