Numerator:
Every fraction has two parts. The top part is called Numerator.
3 

5 

In this example 3 is called Numerator. 
Denominator:
Every fraction has two parts. The bottom part is called Denominator.
3 

5 

In this example 5 is called Denominator. 
Common Denominator:
If you are working on 2 or more fractions and if you are doing addition, subtraction or comparision then it is easy to solve the problem if the denominator is same.
3 

1 

+ 

5 

5 

In this example 5, the Denominator is same in the 2 fractions. So, simply add the 2 Numerators to get the answer. That is add 3 and 1 which is equal to 4 and the answer is 4/5. 
Improper Fractions:
We know that every fraction has 2 parts: Numerator and Denominator. If Numerator is grater than Denominator, then the fraction is called Improper Fraction..
7 

5 

In this example 7 is greator then 5. So, this fraction is called Improper Fraction 