ELI5: What is hate speech?

ELI5: What is hate speech, who decides what is, and why is it illegal in some places but not other places?<br><br>Edit: Thank you for all your answers, I will make sure to pass them along.<br><br>Edit2: I'm sorry if it seemed like I didn't like one of your answers; it's just I want my five year old to be able to understand what I explain to them. You're all great and I love reading your answers!<br><br>Edit3: I'll come back and read all of these once their naps are over.