robot
A robot is a programmable machine that can sense the world around it, decide what to do, and then physically act on that decision by moving or changing something. The key word is physical: unlike an app or a chatbot, which only push pixels and text around, a robot has a body and reaches out into the real world — gripping, rolling, flying, welding, or carrying. A washing machine follows a fixed timer and notices nothing, so it is just an appliance; a robot vacuum that feels a wall, plans a path, and steers around your shoe is closer to the real idea.
Three abilities together make something a robot: sensing (cameras, touch, distance, or position give it information), deciding (a program or a learned model turns that information into a choice), and acting (motors and joints carry the choice out in the physical world). Take away the sensing and you have a blind puppet that only repeats a script; take away the acting and you have a piece of software, not a robot. The same loop scales from a tiny toy up to a factory arm or a self-driving car.
Because the word covers such a huge range, it helps to think in families rather than one fixed image: arms bolted to a factory floor, wheeled or legged machines that roam, drones that fly, humanlike figures, and squishy soft robots. What unites them all is that loop of sense, decide, and act inside a body.
A robot vacuum is a small, complete robot: bump and cliff sensors feel the room, a program decides where to go next, and wheels carry it there.
Sense, decide, act — all in one palm-sized machine.
The word robot first appeared in the 1921 Czech play R.U.R. by Karel Capek — though Karel credited his brother Josef with coining it — where it meant a manufactured worker; it took decades for it to mean a real sensing, acting machine.