Okay kiddo, so you know how you ride your bike to go places? Well, some armies have soldiers who ride bikes instead of driving in cars or tanks. Those soldiers are called bicycle infantry.
Bicycle infantry use bikes to travel around and fight battles. They can ride through really tough terrain that cars and trucks can't go through, and they can move around faster than if they were walking.
When they go into battle, they usually leave their bikes somewhere safe and then fight on foot. But when they need to move to a new location, they can quickly ride to where they need to be.
Bicycle infantry has been used by armies for a long time, especially in wars where there are a lot of hills or mountains or where cars and trucks are hard to come by. They're very good at moving around quietly and quickly, and they're a lot cheaper than using big machines.
So that's what bicycle infantry is, sweetie! Soldiers who ride bikes to get places and fight battles.