Understanding summary fields
A summary field allows you to display information from one or more records. For example, you can add a summary field to calculate the total number of opportunities you lost to a competitor.
When you add a summary field, you select the type of summary field it is:
Count - Displays the total number of records that contain data in the selected field.
Total - Displays the total of all values in the selected field.
Average - Displays the average of all values in the selected field.
Minimum - Displays the lowest or earliest value in the selected field.
Maximum - Displays the highest or latest value in the selected field.
Any field can be added as a Count summary field, but only numeric fields can have a Total, Average, Minimum, or Maximum type.