Sum adds all the values for this field in each group.
Avg calculates the average of all the values for this field (excluding Null values) in each group.
Min returns the smallest numerical value in the field, or the lowest value in collating sequence ("dictionary" order) for text, within each group.
Max returns the highest value in the field within each group.
Count gives the number of rows in which the specified field is not a Null value. (You can also enter the special expression COUNT(*) in the Field row to count all rows in the group, including Null values.)
StDev calculates the statistical standard deviation of all the values for this field in each group.
Var calculates the statistical variance of all the values for this field in each group.