Thermal noise, also known as Johnson-Nyquist noise, is the random electrical noise generated by the thermal agitation of charge carriers, such as electrons, in a conductor. This phenomenon occurs in all resistive materials and is directly related to temperature; as the temperature increases, the level of thermal noise also rises. This type of noise is significant in electronic circuits, especially in sensitive devices like amplifiers and radio receivers. It can limit the performance of these systems by introducing unwanted signals, making it essential for engineers to consider thermal noise when designing electronic components.