What is template symbol?

Typically you would see a sent email symbol under Reports - Reporting - Single Mailing Report - Summary or Clickthrough, but sometimes a template symbol might be seen other places.

The symbol in this user interface is for email type: Sending Canceled. The most likely scenario would be after a email was scheduled, a user went under the Scheduled tab, and unscheduled it (that is, canceled before it was sent to anybody). Or the email might use throttling or STO and was in the Scheduling tab with a "sending" status for some time, and in the middle of sending, a user canceled the send.