(i) Observations:-

Data obtains by the observer from the given problem is called observations.

(ii) Raw data:-

Data collected in its original form is called Raw Data.

(iii) Fequency of an observation:-

Number of times a certain value occurs is termed as frequency.

(iv) Frequency distribution:-

Organisation of Raw data in tabular form is called Frequency Distribution.

(v) Discrete frequency distribution:-

Frequency Distribution in which Raw Data is ungrouped is called Discrete frequency distribution.

(vi) Grouped frequency distribution:-

A frequency Distribution in which Raw data is grouped in specific class.

(vii) Class-interval:-

Class interval is a group under which large number of data is grouped to analyze its Range and Distribution.

(viii) Class-size:-

Class –size is defined as the difference between upper and lower boundaries of any class.

(ix) Class limits:-

Class limits works as separation of one class in a grouped frequency distribution from another.

(x) True class limits:-

The Exact class limits of frequency distribution are called True class limits.