Statistics is a branch of Mathematics which deals with collection, presentation, analysis, interpretation of data and drawing of inferences or conclusions there from.

**Raw or Ungrouped Data:** The data obtained in original form and presented ungrouped without any re-arrangement or condensed form.

**Grouped Data:** Rearrangement or condensed form of data into classes or groups.

**Range of Data:** Difference between the highest and lowest values in the data.

**Frequency:** The number of times an observation occurs in data.

**Class Interval:** Each group in which the observations or values of a data are condensed.

**Class Limits:** Values by which each class interval is bounded. Value on the left is called lower limit and value on the right is called upper limit.

**Class Size:** Difference between the upper limit and the lower limit.

**Class mark of a class interval:** Mid value of a class interval.

**Cumulative Frequency of a class:** Total of frequencies of a particular class and of all classes prior to that class.

**Bar Graph:** A pictorial representation of data in which usually bars of uniform width are drawn with equal spacing between them on one axis and values of variable (frequencies) are shown on other axis.

**Histogram:** A pictorial representation like bar graph with no space between the bars. It is used for continuous grouped frequency distribution.

**Frequency Polygon:** A graphical representation of grouped frequency distribution in which the values of the frequencies are marked against the class mark of the intervals and the points are joined by line segments.

**Central Tendency:** A Single quantity which enables to know the average characteristics of the data under consideration. Use of central tendency is a technique to analyse the data. Various Measures of central tendency are mean (average), median, and mode.

**Mean:** It is the ratio of the sum of all values of the variable and the number of observations.

**Median:** It is the middle most value of arrayed data. It divides the arrayed data into two equal parts. Arrayed data is in ascending or descending order of magnitude.

**Mode:** It is the most frequently occurring value among the given values. It is an observation with the maximum frequency in the given data.