Mathematical term for the square root of a number. Equivalent to 平方根 (へいほうこん), but 二乗根 is less common in everyday math contexts.
The square root of 4 is 2.
立方根 means 'cube root', the root of degree 3, while 二乗根 is specifically the square root (degree 2).
Compound of 二乗 (にじょう, 'squared') and 根 (こん, 'root'), literally 'squared root'.