Absolute zero is the presence of a true zero on a number scale. A scale with absolute zero is the most informative and accurate scale to use for measurement, but only a ratio scale has an absolute zero.
For example, when counting money, $10 is twice the amount of $5, and $0 is the complete absence of money. So money can be measured with a ratio scale. But temperature in degrees Fahrenheit cannot be measured with a ratio scale because 0 degrees F does not represent the complete absence of temperature. The Fahrenheit scale lacks an absolute zero.