An operation that needs two inputs.
A simple example is the addition operation "+":
In "2+3=5", the operation is "+", which takes the two values "2" and "3" and gives the result "5".
Subtraction, multiplication and division are also binary operations, and there are many more.
The two inputs are called "operands".
A binary operation should take and return things of the same type!
In other words, the operands and the result must belong to the same Set.