It isn't! It's a short approximation to pi, which has an infinite decimal expansion. Here are a few more decimals:
π=3.1415926535897932
All fractions can be written as terminating or recurring decimals.
Any number that can be written as a fraction, pq , is a rational number.
π is an IRRATIONAL NUMBER. This means it cannot be written exactly as a fraction or as a terminating or as a recurring decimal. The numbers just keep going forever and they never form a pattern!