Speech crimes are bad things you say that can get you in trouble. Just like hitting or stealing can be a crime, something you say can also be a crime.
Speaking kindly and respectfully to other people is important. If you say something mean or hurtful to someone, that's not nice and it might get you in trouble. There are also things that you can't say because they will make other people feel bad or scared.
For example, if you say something scary that makes someone else worry that they might get hurt, that could be a speech crime. If you say something mean about someone's race or religion, that can also be a speech crime.
It's important to always think before you speak and say nice things to others. If you're not sure if something you want to say might be a speech crime, it's best to keep your thoughts to yourself or ask a grown-up for advice.