Something like 3.5 = 7/2 is a rational number because its a fraction of two integers.
While on the other hand, the constant pi = 3.14159... is irrational because we cannot write pi as a fraction of two integers. We can get approximations like 22/7, but not a perfect exact match.
Both types of numbers, rational and irrational, are under the umbrella of the real number system. Any real number is a string of decimal digits. Sometimes it might be a whole number, but fractional values can be included as well. The decimal number may terminate, or it may repeat, or it may go on forever without a pattern.
In short, any number you can think of is a real number assuming your teacher hasn't covered complex numbers (or imaginary numbers) just yet.
