Bertillon is a way to measure and describe people so that we can tell them apart from others. It was created by a man named Alphonse Bertillon a long time ago. He thought that if we had a system to measure different parts of a person's body, we could use those measurements to identify them.
So, imagine if you and your friend had the same name and looked really similar, like twins. People might get confused and not know who is who. But if we measured different parts of your body, we could find some differences. For example, we could measure how tall you are, how long your arm is, and how big your head is. These measurements would be different even if you and your friend looked really similar.
Bertillon came up with a whole set of measurements to help identify people. He measured things like the length of your head, the length of your arm, the width of your nose, and the size of your foot. He even measured things like the distance between your eyes or the length of your ear. All these measurements would be unique to each person, just like fingerprints.
To use Bertillon, someone would take all these measurements and write them down on a card. This card would have your name, your age, and other information about you. It would also have a picture of you, so people could see what you look like. This card would be kept safe, just in case we needed to find you or prove that you are who you say you are.
Back in the old days, before we had computers, Bertillon measurements were very helpful for the police. If a person committed a crime, the police would use these measurements to try and find the criminal. They would compare the measurements of the suspect to the ones they had on the card. If the measurements matched, they would know that they found the right person, and they could catch the criminal.
But now, we have better ways to identify people, like fingerprints and DNA. These methods are more accurate and reliable, so we don't use Bertillon measurements as much anymore. But at the time, Bertillon was a big step forward in helping us tell people apart and catch bad guys.