In mathematics, a rational number is a number that can be expressed as the quotient or fraction ⁠⁠ of two integers, a numerator p and a non-zero denominator q. For example, ⁠⁠ is a rational number, as is every integer. The set of all rational numbers is often referred to as "the rationals", and is closed under addition, subtraction, multiplication, and division by a nonzero rational number. It is a field under these operations and therefore also called the field of rationals or the field of rational numbers. It is usually denoted by boldface Q, or blackboard bold ⁠⁠