Programming is the art and science of writing sequences of instructions ("programs") for a computer to tell it what to do.
That ranges from writing Web sites, to apps that run on your computer, phone, tablet, games console, or the software inside tiny computers that make household appliances and cars and things like that work.
Perhaps a good place to get started with programming for hackerly folks is the Arduino. It's a little computer you can write programs for on your laptop and then download them to it, and then it'll run off of a battery or small mains power supply, and be able to control all sorts of lights, sensors, motors, and so on. It's very popular as a controller for robots, fancy lights and displays, and all manner of homebrew gadgets; and it has an easy to learn programming environment.