A bayonet is a special tool that soldiers use with their guns. It looks like a long and pointy knife that can be attached to the end of a gun. This makes the gun into a weapon that can be used for stabbing, just like a regular knife.
Bayonets were first invented a long time ago when soldiers used guns that took a really long time to reload. If they ran out of bullets or needed to fight up close, they could use their bayonets to keep fighting. Now, soldiers have much faster guns, but bayonets are still used because they can be very helpful in certain situations.
The word "bayonet" comes from the French word "baïonnette," which was named after a town in France where they were first made. So, even though they are often used by soldiers from all over the world, the word for them comes from France!