Resistance is defined as the opposition to current flow. The unit of measure for resistance is the ohm, which is symbolized by the greek letter omega:
The ohm is named for George Simon Ohm who discovered the relationship between current, voltage and resistance. The electrical symbol is:
Materials with low resistance (less than 10 ohms), are considered to be conductors. Materials with high resistances (greater than 10 Mega-ohms - 10,000,000 ohms) are considered to be insulators. Good conductors are materials like copper, gold and silver. Good insulators are materials such as glass, rubber and mica.
Resistors used in electronics are of 3 basic physical types: