A cathode ray tube (CRT) is a device that was commonly used in older televisions and computer monitors. It works by firing electrons from a cathode, which is a negatively charged electrode, towards a phosphorescent screen. When these electrons hit the screen, they create images by lighting up specific areas. CRTs were popular for many decades due to their ability to produce bright and clear images. However, they have largely been replaced by newer technologies like LCD and LED displays, which are lighter, thinner, and more energy-efficient. Despite this, CRTs played a significant role in the development of modern display technology.