The SharePoint Inactive Objects report shows you the number of ibjects that have been modified within a given time period.
Changing the Time Period
The time period selector above the graph allows to to specify what constitutes an "Inactive Object".
For example, if you click the 30 Days button the report will display all objects that have not been modified for 30 days or more.
The All Button
Selecting the All button will display a breakdown of the Last Modified dates for all objects.
The Data Table
The data table will show all Inactive Objects within a certain time period as well as the its Last Modified Date.
If you select the All button, it will display this information for all objects.