On a Kelvin thermometer, absolute zero is simply "zero." On a Celsius thermometer, absolute zero is at -273 degrees. Absolute zero is the lowest temperature in the world, and has never actually been attained in a laboratory.

Give me an example!

When you freeze water into ice, the molecules form a solid crystalline structure and move much less than when the water is in its liquid phase. If you continue to lower the temperature of the ice, you will reach a point where all molecular motion comes to a standstill - theoretically, at absolute zero.