Definition
An electron tube, also known as a vacuum tube or thermionic tube, is a device that controls the flow of electrons in a vacuum. It's made of a sealed glass or metal enclosure containing electrodes. Electrons are emitted from a heated cathode and controlled by electric fields created by other electrodes. Electron tubes were widely used in early electronics for amplification, switching, and signal processing. Though largely replaced by semiconductors, they still find niche applications. They serve as a key step in creating smaller transistors and circuits.