Explanation: Statistics represents data aggregation of the metric data values over a specific period of time. The user can specify the start and end times that CloudWatch will use for the data aggregation of the statistics. The starting and ending points can be as close together as 60 seconds or as far apart as two weeks.
Reference:
http://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/ cloudwatch_concepts.html#Metric