A transistor amplifier is an electronic device that increases the strength of electrical signals. It uses a transistor, which is a semiconductor component, to control the flow of current. By applying a small input signal, the amplifier can produce a larger output signal, making it useful in various applications like audio equipment and radio transmission. Transistor amplifiers are essential in modern electronics, as they help improve sound quality and signal clarity. They can be found in devices such as microphones, guitars, and televisions, where they enhance weak signals for better performance.