Resistors are electronic components, which offer resistance against the current flow, or speaking at a deeper level, against the electrons' flow. Resistors, denoted by R, are passive components, which means that they don't generate any electricity at all, but rather reduce voltage and current by dissipating power in the form of heat.

The unit of resistance is ohms (Ω) and resistors are usually built using carbon or metal wire. You will also find the resistors being color-coded in order to help convey the value of resistance they offer.

This is what a resistor looks like:

Now that you know what resistors are, it is also worth noting that there could be two different categories of resistors-fixed and variable. As the name implies, a fixed resistor is where the resistance is fixed and cannot be changed, whereas in a variable resistor, the resistance can be varied using certain techniques. One of the most popular examples of a variable resistor would be a potentiometer.