Assignment of security to content.
Permission is the assignment of security to content. A user is either authorized to read, contribute or own content or not authorized to access the content. Permission can be set on all levels in SharePoint from site collection to individual item.
Default permission levels are predefined sets of permissions that you can assign to individual users, groups of users, or security groups, based on the functional requirements of the users and on security considerations. SharePoint Server permission levels are defined at the site collection level and are inherited from the parent object by default. You can read more about default permissions in sharepoint, here.
Questions having the tag permissions regards every aspect of permission to content.