Imagine you are going on a very long trip to a new planet far away, but you can't just fly there like in an airplane. Instead, you have to travel in a sleeper ship.
Now, a sleeper ship is a special kind of spaceship that is built to travel long distances. But the trip could take many years, and who wants to stay awake that long? That's where the "sleeper" part comes in.
On a sleeper ship, you get to sleep for the whole journey. Think of it like taking a really long nap, but inside a spaceship. You are put into a special sleeping pod - a bit like a very cozy, high-tech bed.
This pod will keep you asleep and healthy for the whole journey, supplying all the food and oxygen you need. It's kind of like a magic bubble that keeps you safe and healthy while you sleep.
So, for example, if it takes 50 years to get to the new planet, you might go to sleep when you are 20 years old, and wake up when you are 70! But you won't feel any older. Your body will stay just the same as when you went to sleep, because you are technically frozen in time. When your pod opens, you'll feel like you just closed your eyes for a minute, even though decades of time have passed.
That's why sleeper ships are really important for space travel - they allow people to travel long distances without aging, and without getting bored. It's like sleeping through a really long car ride, but in space!