When you are building a metric, you have the choice of how to calculate the metric score. Your options are:
SUM: Sum of the VALUES in the field of your choosing. Usually how Pipeline and Closed Won metrics are calculated.
COUNT: Add the total number of records that meet metric criteria. Usually how Tasks are calculated.
COUNT DISTINCT: NEW! Count the UNIQUE number of records that meet your criteria. As an example (below), you can count Tasks for the day that meet criteria but when there are many Tasks for each Account, you may count ONE Task PER Account. This would mean the tasks were unique account touches.
MIN: Lowest value of a field of your choosing. For example, lowest Closed Won Opp this month.
MAX: Highest value of a field of your choosing. For example, highest Closed Won Opp this month.
AVERAGE: Average of all values in a field of your choosing. For example, average dollar amount of Closed Won this month.