A speedster is a fictional character who can run really, really fast. They are often superheroes or villains in comic books and movies. They have the ability to move at incredible speeds, which makes them super awesome and also makes it pretty hard for bad guys to catch them!
Imagine you are playing tag with your friends and you are really good at running. You can easily run really fast and dodge your friends when they try to tag you. That is kind of like how a speedster works, except they can run really, really fast - even faster than a race car sometimes!
Speedsters have some cool abilities that come with their super speed. They can sometimes use their speed to travel through time or create whirlwinds with their running. They can also run up walls or across water, because they are so fast they can overcome normal physics.
Speedsters are cool because they can save people really quickly, and they can zoom around to fight crime all over the place. They are like superheroes with an extra-fast superpower!