Frequency distributions are a way of organizing and summarizing data. They show how often each value or category occurs in a dataset.

There are two types of frequency distributions:

1. Ungrouped frequency distribution: This type of distribution is used when the data is discrete and the values are not too many. In this case, the data is listed in order and the frequency of each value is recorded.

Example:

Suppose we have the following data representing the number of hours students study per day:

2, 3, 2, 4, 1, 3, 2, 3, 4, 2

The ungrouped frequency distribution would be:

Number of Hours | Frequency
--- | ---
1 | 1
2 | 4
3 | 3
4 | 2

2. Grouped frequency distribution: This type of distribution is used when the data is continuous and the values are too many. In this case, the data is grouped into intervals or classes and the frequency of each interval is recorded.

Example:

Suppose we have the following data representing the weights of 20 students in kg:

52, 55, 60, 63, 65, 67, 68, 70, 72, 74, 75, 77, 78, 80, 82, 83, 85, 87, 90, 92

The grouped frequency distribution with class width 5 would be:

Weight (kg) | Frequency
--- | ---
50 - 54 | 2
55 - 59 | 2
60 - 64 | 2
65 - 69 | 3
70 - 74 | 3
75 - 79 | 3
80 - 84 | 2
85 - 89 | 2
90 - 94 | 1

Frequency distributions can be presented in different forms such as tables, histograms, or frequency polygons. They are useful in identifying patterns and trends in data, and in making comparisons between different datasets.