What Is The Number 3.142 More Usually Known As Pi (Pronounced 'Pie' - It Represents The Ratio Of A Circle's Circumferance To Its Diameter, Also Expressed By The Fraction 22/7, And The Sixteenth Letter Of The Greek Alphabet, Pi, Equating To 'P', And Shown As The Symbol P . The Number 3.142 Is A Rounding To Three Decimal Places; The Full Decimal Number Of Pi Is Infinitely Long And Cannot Be Expressed Absolutely Other Than As A Fraction.