The Activity Log provides a record of the changes and actions that have been going on within the website.
Your assigned Administrators are able to access the Activity Log to check up and see what's been happening within the website and to see who has been working on it.
Here is an example of what the Activity Logs look like:
Accessing the Activity Log
You can find the Activity Log link in the top right of the page while you are logged into the Admin System, as shown with the red box below.