In this post we will discuss about user information list in SharePoint 2010. Also you can check out my previous posts on:
User Information List is a hidden list maintained by SharePoint 2010 to stores and maintains a user information profile for authenticated users at the site collection level. A user also can update the profile information from the My Settings link. So for a particular user there will be only one user profile information accross all the sites in the site collection.
The information may be like email, displayname, loginname etc.
You can see the list from the below URL
SPList userInformationList = SPContext.Current.Web.SiteUserInfoList;
But if you are using SharePoint Server and you have configured User Profile Service application to import profiles, in that case the information are copied from User Profile to User Information List by two timer jobs "User Profile to SharePoint Full Synchronization" and "User Profile to SharePoint Quick Synchronization". Here your profile information can be updated from the Active Directory or from My site feature.