So far, this has only been reported by Deadspin, but the investigation they conducted appears compelling.
The girlfriend of Notre Dame linebacker Manti Te'o, who was reported as having passed away during the season and served as an inspiration to Te'o during the team's championship run, is allegedly a hoax created by Te'o and a close friend for publicity purposes.
There are no records (newspaper obituaries, publicly accessible government records, etc.) of anybody with his alleged girlfriend's name dying in 2012.
The pictures associated with his girlfriend's Twitter account (which Te'o himself has Tweeted to) are confirmed by Deadspin to have come from the Facebook account of a young woman who has never met Te'o but knows one of his good friends.
Expect this to become a bigger story as mainstream news outlets conduct their own investigation.