The IMABS() function in Google Sheets is used to find the absolute value (magnitude) of a complex number. A complex number is a number that includes a real part and an imaginary part, and is represented in the form of a + bi, where a is the real part, b is the imaginary part, and i is the imaginary unit (where i^2 = -1).

The IMABS() function takes a complex number as its argument and returns the magnitude of that number, which is calculated as the square root of the sum of the squares of the real and imaginary parts of the number. The result of the function is always a positive real number.

For example, the IMABS() function applied to the complex number 3+4i would return the value 5, which represents the distance of the number from the origin in the complex plane.