Resistors are one of the most common components in electronics, if not the most common components. They have a specific resistance that is very useful for a wide variety of reasons. They have varying values of resistance, from milliohms to megaohms, as well as different packages from tiny surface mount devices that you can barely see up to large chassis mounted packages that can handle thousands of watts of power. They also have varying precisions, from guaranteeing to be only within 10% of the stated value to .01% precision. Of course, higher precision costs more, so there’s always a trade-off.