Custom Permission - Custom permission are the feature which allow the user to provide the extra functionality which is not covered by the profile and the permission set. 

You have a custom permission called "Access_Special_Report_Permission" that controls whether a user can view a special report.

To Create a the Custom permission the following steps are given

1 From Setup Quick Search Enter the Custom Permission



2) Click on New



3) Enter the value and the api name of the package of the custom permission



4) then click on save

5) Search for profile in the quick search and in the custom permission we can add the permission




For more information you can check the Blog - https://salesforceh.blogspot.com/


Reference - https://help.salesforce.com