A "ghost follower" on Instagram is a user who follows an account but does not ever interact with the account (by liking or commenting on the account's photos.) Many popular Instagram users are taking steps to block or discourage ghost followers.
Ghost followers may be users who have gone inactive on the service or who passively view photos without liking or commenting. However, many ghost followers are spam blogs or scammers attempting to search the site for victims. Another motivation for ghost following occurs when users follow random accounts in the hopes of being followed back and increasing their own popularity on the site, even though they may have no genuine interest in the account they followed.