From Computer History Wiki
A resistor is a passive element in an electrical circuit which impedes the flow of current through the resistor.
The relationship between the voltage across the two connectors of a resistor, the current through it, and the degree of resistance is given by Ohm's Law, which states that the current (in amperes) is equal to the voltage (in volts) divided by the resistance in ohms (the unit being named in honour of the discoverer).
Resistors convert a portion of the current flowing through them into heat; the amount (in watts) is equal to the current (in amperes) squared, times the resistance (in ohms).
Resistors show the same impedance to direct current as they do to alternating current, of any frequency.