Active cylinder control is like when you have a big box of Legos and you can choose which pieces to use. A car engine has a bunch of cylinders that work together to make the car go. But sometimes you don't need all the cylinders to work because you're just driving slow or not going up a hill.
Active cylinder control is when the car's computer can turn off some of the cylinders and just use a few of them to save energy. It's like if you only use a few Legos from the box instead of all of them. This can help the car use less gas and be better for the environment.
But if you start going faster or up a hill, the computer will make all the cylinders start working again so the car has enough power to keep going. It's like if you need more Legos to build something bigger or taller, you start using all of them again.
So, active cylinder control is when a car's computer helps it save energy by only using some of the cylinders when it doesn't need all of them, and then using all of them again when the car needs more power.