The document provides an overview of number systems used by different civilizations. It discusses ancient number systems including the Egyptian use of base-12 and Babylonian use of base-60. The decimal system is introduced as the most common modern system using base-10. Other number systems mentioned include binary, Mayan vigesimal, and fractions in ancient Egypt. Real numbers are defined as including integers, rational numbers like fractions, and irrational numbers like pi. Terminating, non-terminating recurring, and non-terminating non-recurring decimals are also briefly explained.