In Salesforce, a Rollup summary is a field that calculates the total value from a range of connected records. There are various functions you can input into a Rollup summary field, which are:
Count: This calculates the total number of records within a specific parameter
Sum: This function adds together the entire values of the selected data fields
Min: The min function shows the lowest value of those selected
Max: The max function shows the highest value of those selected
