Transmission is the process of sending or passing something from one place or person to another. When a radio station broadcasts a program, it's sending out a transmission of radio waves that your radio receives. When you catch a cold from a classmate, that's disease transmission: germs traveling from one person to another.

The word appears in many contexts. In a car, the transmission is the machinery that transfers power from the engine to the wheels, making the car move forward or backward. Engineers talk about power transmission when electricity travels through wires from a power plant to your house. Scientists study the transmission of light through different materials, like how sunlight passes through a window but not through a brick wall.

Transmission often suggests something invisible or automatic happening: information transmitting through a computer network, heat transmitting through metal, or a television signal transmitting through the air. It always involves something moving from here to there, whether it's energy, information, or illness.