What is a operation in math?

Answer 1

An operation is a function. It takes one or more numbers and returns another number or set of numbers. Given the same inputs the operation will produce the same output(s).

Binary operations are one that take two numbers as input and the output is one number. Addition, subtraction, multiplication, division are familiar examples.

But operations need not be Binary: The usual method of calculating the distance between two points whose coordinates in a plane are known, takes an input of 4 numbers and outputs 1.

Also, the output need not be just one number: The muliplication of two complex numbers takes in 4 numbers and outputs two (the real part and the imaginary part).