A resistor is a passive two-terminal electrical component that introduces electrical resistance to a circuit. They reduce current flow, adjust signals, divide voltages, and more. Resistors dissipate electrical power as heat, with resistance measured in ohms according to Ohm's law.
Resistors are ubiquitous in modern electronics, and critical components in just about every electrical device. Because their primary purpose is to limit current, and the type, size and materials used to describe the resistor play an important role in how the resistor behaves in the circuit. Larger resistors can dissipate more power as heat and withstand high temperatures, suitable for high-power applications like motor braking and power transmission. Smaller resistors with a metal foil design limit less current but provide the highest degree of precision and stability, making them more useful in sensitive circuits that are susceptible to excess noise.
Most resistors are simply built-in to most modern components like integrated circuits and microprocessors, but many standalone options are available to provide a variety of panel and circuit board solutions.