Avenir is a fancy way of saying "font" or "letter style" that people use on their computers. It's like having different types of handwriting that you can choose from when you write a letter. Avenir is a pretty popular font that you might see in different places like on signs or in books. It has a clean and modern look with straight lines and smooth curves. It's easy to read and looks nice when you use it for titles or headings. Just like how you can choose what color crayon you want to use when coloring, you can choose what font to use when writing.