Definition: User Information list is a hidden list in SharePoint which is available in all the site collections but is accessible to Site Collection Administrator only.

User Information List stores information like User Id, User Name, Email, Location, Designation, etc...

Whenever a user is granted access on Site Collection, an entry is created for that Active Directory user in User Information List (if the entry of the user is not already there.)

User Information list can be accessed by going to below path in Site Collection.

https://ServerName/SiteURL/ _catalogs/users/simple.aspx