Text mode is a way that a computer can show text on the screen. Imagine looking at a big sheet of paper with nothing but words on it, that's what text mode does, but on a computer screen.
In text mode, the computer only shows letters, numbers, and symbols. It's like a regular book or newspaper, but on a screen. There are no pictures or colors, just black and white letters on a plain background.
Text mode is useful because it allows the computer to show a lot of text at once and it's easier to read than if everything was mixed together with pictures and colors. It's also a faster way for the computer to display information since it doesn't need to worry about extra details like colors and graphics.
So next time you see just plain old letters and numbers on your computer screen, you'll know it's using text mode.