iostream is a fancy word that means a way for a computer to talk to you and listen to what you say. When you use iostream, you can tell the computer to show you things on the screen or ask you questions, and then you can tell the computer what you want it to do based on what it says back to you.
Think of it like talking to a friend over the phone. You say something and then your friend responds, and then you respond based on what they said. iostream works the same way, but instead of talking over the phone, you're talking to a computer.
This can be really helpful for programmers who want to create programs that interact with people. With iostream, you can create programs that ask questions and get responses, show messages on the screen, and do all sorts of other cool things. It's a way for computers to communicate with people in a way that's easy to understand.