The Ignored users list is a list containing users that a particular user wishes to ignore. Users may be added to ignored user lists if they post unfavorable reviews, or if they send messages that another does not like. Every user has his/her own ignored user list, and this list is invisible to all other users with the exception of admins and moderators. The only way to ignore a user is using Ban/Unban user in his profile. Users can view their ignored user list on their profile.
You can un-ignore a user by clicking remove in the Ignored users list as well as click Ban/Unban user on an ignored user. A moderator also has the ability to remove a user from your ignored user list.