"The product of any two real numbers is also a real number" is one of the condition in what binary operation?

The statement "The product of any two real numbers is also a real number" describes a property of the binary operation known as multiplication. In the context of real numbers $\mathbb{R}$, multiplication is defined as a binary operation that takes two real numbers $a$ and $b$ and produces another real number $a \times b$.

This property is part of the closure property of multiplication in the set of real numbers. Closure under a binary operation means that performing the operation on members of the set results in a member of the same set. In simpler terms, when you multiply any two real numbers, you always get another real number, thereby demonstrating that real numbers are closed under multiplication.

To summarize, the product of any two real numbers being also a real number is a characteristic of the multiplication binary operation applied to the set of real numbers.