A courtesy title is like a special name that people sometimes use to show respect or politeness. Just like you might call your grandma "Nana" instead of just her first name because it's a way to show her that you love and appreciate her.
For example, sometimes people call doctors "Dr." or teachers "Ms." or "Mr." This is a way to show respect for their hard work and knowledge.
These titles are called courtesy titles because they are a way to show courtesy, which means being polite and respectful to other people. It's important to use them to show people that you appreciate them and to be polite to them.