(i) Variate: Any character that can vary from one individual to another. 

(ii) Class-integral: In the data of each group into which raw data is considered. 

(iii) Class-size: The difference between the upper limit and lower limit. 

(iv) Class-mark: The middle value of the selected class. 

It can be calculated as : 

Class-mark = (Upper limit + Lower limit) /2 

(v) Frequency: The number of observations corresponding to class. 

(vi) Class limits: Each class is bounded by two figures, called the class limits. The figure on the right side are called upper limit while figure on the left side of the class are called lower limit. 

(vii)True class limits: 

If classes are inclusive. For example: 5-9, 10-14, 15-19 and so on 

Then, true lower limit of class = Lower limit of class – 0.5 

And, true upper limit of class = Upper limit of class + 0.5 

In this case, True limits of the class is 5-9 are 4.5 and 9.5 

But if classes are exclusive like 20-30, 30-40, 40-50 and so on, then class limits and true class limits are the same.