A dumb terminal is like a computer, but not as smart. It is like a monitor and a keyboard, but it doesn't have its own brain. Instead, it needs another computer to tell it what to do.
Imagine you have a toy that you can only move if your mom tells you what to do. That's like a dumb terminal. It needs a bigger computer, called a mainframe or a server, to tell it what to do.
The server has all the brains and can do all the work. It sends instructions to the dumb terminal, and then the terminal shows you what the server wants you to see.
So, if you're looking at a computer screen right now, imagine that the computer is telling the screen what to show you. Now, imagine the screen is your whole computer - that's what a dumb terminal is like!