A negative rational number is a rational number less than zero. This is illustrated on a simple number line on which all numbers to the right of zero are positive, and all numbers to the left of zero are negative. Negative rational numbers are to the left of zero.
A rational number is any number that can be written as a fraction, of which the numerator and denominator are real numbers, and the denominator is not zero. For example, 1/3 is a rational number, but 3/0 is not. The number 9 is rational because it can also be written as 9/1. Numbers that are not rational are called irrational, and some examples are pi and the square root of three.