irrational number
A real number that cannot be expressed as a simple fraction. Used in mathematics.
√2 is an irrational number.
無理数は分数で表せない数です。
Irrational numbers are numbers that cannot be expressed as fractions.
Compound of 無理 (muri, 'unreasonable') + 数 (sū, 'number'), literally 'unreasonable number'. The term is a calque from Western mathematics.