Imagine a really tall mountain that reaches up into the clouds. It's so tall that it's even taller than most airplanes fly! That's what we call an eight-thousander.
You see, a group of people called mountain climbers really like to climb these tall mountains. But not all mountains are created equal. The mountains that are eight-thousand-meters tall or taller, which is about 26,247 feet, are called eight-thousanders.
Now, climbing an eight-thousander is not like taking a walk to the park. It can take weeks or even months to get to the top! The air is very thin up there, which means that it's harder to breathe, and that means climbers have to wear oxygen masks.
But the view from the top makes all of the hard work worth it! And the best part is that only a few people in the world have ever climbed to the top of all 14 eight-thousanders.