Okay kiddo, so imagine you're in a boat with your family and suddenly the boat starts to sink. Your parents might yell "mayday! mayday!" into a radio or phone to ask for help from someone who can rescue you.
Mayday is a special code word that people use to show that they are in an emergency and need help right away. It is like a very big alarm that sends a message to everyone listening that someone is in trouble and they need help.
People who work on boats or planes or in other jobs where they may need emergency help use this word to get help fast from other people nearby who can come and save them.
So, remember that if you ever hear someone say "mayday," it means that someone needs help really urgently, and it's important to listen and be ready to help them.