Demo is short for demonstration, which means showing someone how something works or what it can do. When a salesperson gives you a demo of a new video game, they play it in front of you so you can see the graphics, gameplay, and special features before deciding whether to buy it. When a science teacher performs a demo with baking soda and vinegar, the class watches the fizzing reaction happen right before their eyes.

Demos make abstract ideas concrete. Instead of just reading about how a chemistry experiment works, you watch it bubble and change color. Instead of hearing someone describe a new app, you see them tap through the screens and watch what happens.

The word appears in many contexts: software companies release demo versions of programs that let you try limited features for free. Musicians record demo tapes of new songs to share with record labels. A cooking show host might demo a new kitchen gadget by actually using it to chop vegetables on camera.

Notice that demos are always active: someone is doing something while others watch and learn. A demo isn't a lecture or a description. When you demo something, you're proving it works by making it happen in real time.