A pentode is a type of electronic vacuum tube that contains five active elements: a cathode, an anode, and three grids. These components work together to amplify electrical signals. The additional grids help improve performance by reducing unwanted effects, such as distortion and noise, making pentodes suitable for various applications, including audio amplification and radio frequency circuits. Pentodes are commonly used in audio amplifiers and radio transmitters due to their ability to provide high gain and efficiency. They are often preferred over other tube types, like triodes, because of their superior linearity and stability in signal amplification.