In a basic CW transmitter, what does the key do?

In a basic continuous wave (CW) transmitter, Morse code is generated by turning the unmodulated radio frequency (RF) signal—known as the carrier—on and off. The telegraph key acts as the switch that controls this specific action. When the key is pressed down, the carrier wave is transmitted to the antenna, creating a "mark" (a dot or a dash). When the key is released, the carrier is turned off, creating a "space" between the marks. Distractors suggesting the key switches a "tone" are incorrect because a CW transmitter sends a pure RF carrier, not an audio tone over the air. The audio tone is actually generated later by the beat frequency oscillator (BFO) inside the receiving station's radio.