A transistor amplifier is an electronic device that increases the strength of a weak electrical signal. It uses a transistor, which is a semiconductor component, to control the flow of current. By applying a small input signal to the transistor, it can produce a larger output signal, making it essential in various applications like audio equipment and radio transmitters. Transistor amplifiers come in different configurations, such as common emitter, common collector, and common base. Each configuration has unique characteristics that affect gain, input, and output impedance. These amplifiers are crucial in modern electronics, enabling clearer sound and better signal transmission in devices like smartphones and televisions.