Rational numbers terminate or repeat. For example
Rational numbers:
3.444444... (4 repeats on forever, therefore this number is rational)
5.7 (The decimal terminates after 7, therefore this number is rational)
Irrational numbers:
3.14159265358979323846....(The number continues on in an unpredictable way, and doesn't terminate or repeat at any point. Therefore this number is irrational)
Hope this helps!