A Unique Visitor who makes a purchase. A Unique Customer is counted once for that time frame but cannot be counted again, no matter how many times the visitor returns to make a purchase. A Unique Visitor is counted once for the first visit in a specified period and not counted again until the period expires. After the period expires, the Unique Visitor is counted again. Unique Customers are always counted as Unique Visitors because they must visit the site in order to make the purchase.
Period-based Unique Customers (Hourly, Daily, Weekly, and so on) reports are also available, similarly to period-based Unique Visitors reports.