Trend Explorer lets you see how often any pre-defined topic was mentioned on any given day.
We count up the number of messages that have a given topic. For a message to have a topic associated with it, it must contain keywords or phrases associated with that topic. For example, you can see in the screenshot that that there were 12 messages related to bug_reports, and 3 messages related to account_issues on November 8th
To learn more about topics check out: