A jammer is like a special kind of swimsuit that people wear when they go swimming or racing in the water. It is basically like a pair of tight shorts that goes down to your knees, but it's made out of special material that helps your body move through the water faster.
The material is very stretchy and smooth, which lets you move your legs and kick really easily while you swim. Plus, it helps reduce water resistance, which means you can swim faster overall.
People who wear jammers are usually swimmers or professional athletes who need that extra speed boost to perform their best. But anyone can wear them if they want to feel comfortable and confident while they swim!