Thermionic valves, also known as vacuum tubes, are electronic devices that have been in use since the early 1900s. They are used in a variety of applications such as amplifiers, radios, and television sets. There are several synonyms for the term thermionic valve, including electron tube, vacuum tube, and CRT (cathode ray tube). The concept of a thermionic valve is based on the flow of electrons from one electrode to another. These synonyms are often used interchangeably in technical literature and discussions related to electronics. Despite the rise of solid-state technology, thermionic valves continue to be used in niche applications and are appreciated by enthusiasts for their unique sound quality and aesthetics.