What is Autogroup and Summarize?

This is a query property that governs how transactional data is reported. If you are looking for this property, it is on the query property sheet. See image below.
For example: If Auto group and Summarize= NO, the report or query output would be something like this: Auto group and Summarize= YES, the report or query output would be something like this:

So, auto group and summarize basically groups the lowest level in the query and summarizes the measure for the same.
Note: Auto Group and summarize until version Cognos 8.2 had some bug and would generate incorrect queries. This had to be set to “No” to validate the report. :-(