So, these are the various permissions available in SharePoint. A quick glance of course.
Why? Because I believe this is easier(for me anyways) to look and stop freaking out when one entertains the thought that a visitor of their site modified their style template and deleted their custom pages(ahem.. I never do that btw!)
So, there ya go! Trust this helps folks. Stay secured and worry free in your SharePoint collaboration space!!
You can learn more about additional permission settings from Microsoft Technet article.