A letterhead is like the fancy clothes that people wear to look official and important when they go to important events.
When you write a letter, you can make it look fancy and important by putting the name of your company or organization at the top, along with the address, phone number, and sometimes a logo. This is called the letterhead.
Just like wearing your fancy clothes can make you feel important and confident, using a letterhead can make your letter look important and make the person who receives it take you more seriously. Plus, it helps the person know who the letter is from right away.