Okay, you know how when you ride your bike, you move your legs to make the wheels go round and take you to where you want to go? Well, there are some grown-ups who like to ride bikes too, but they do it really, really fast and they ride in circles on a special track.
At the UCI Track Cycling World Championships, which is like a big competition for these grown-ups, there's a special race called the women's keirin. In this race, six women on bikes start off behind a little motorbike called a derny. The derny goes faster and faster until it reaches a certain speed and then it pulls off the track and the women start sprinting really hard.
But here's the catch: the women are not allowed to go in front of each other until a certain point in the race. They have to ride close behind each other, almost touching, until a bell rings, and then they can start trying to pass the person in front of them.
The race is only two laps long, and it can get really exciting because the women have to make quick decisions about when and how to try to pass each other. The winner is the first person to cross the finish line.
So, in short, the women's keirin is a bike race for really fast grown-ups, where they have to sprint and ride close together until a certain point in the race. It's a short and exciting race to watch at the UCI Track Cycling World Championships.