Do you know what a factory is? It's a big building where things are made by lots of people working together. When the things are all made, the people need to put a mark on them to show where they were made. This mark is called a "factory mark".
Think of it like when you color a picture at school. When you're finished, you write your name on it so that everyone knows you made it. The factory mark is like the name on the pictures you color. It helps people know where the thing was made and who made it.
So, if you ever see a toy, a piece of clothing, or something else with a mark on it that says "Made in USA" or "Made in China" or "Made in India", that's a factory mark. It tells you where the thing was made!