People used to share accounts for PS3 games, now they're doing the same for PS4 games, to cut back expenses.
It's only safe to do it amongst friends, though. Don't trust e-bay sellers.
Someone creates a new account, purchases one game on it and then the game can be shared to up to three people, and they split the cost of it accordingly.
Here's how it works:
Ghost Player (Pays 30%)
The ghost player receives the account and downloads the game.
Whoever is mediating the transaction then goes to the sony website and revokes his console permission to use the account.
Therefore, the ghost can never re-download the game if something happens, but the ghost can play with any PSN ID.
Secondary Player (Pays 20%)
The secondary player logs in with the account, sets his console as secondary, then downloads the game to the console. He will always be able to re-download the game, but he will never be able to play the game with his original PSN ID. He will only be able to play it using the new account created specifically to buy the game. So this isn't good if you're a completionist and really enjoys hunting trophies, because they won't go to your PSN ID.
Primary Player (Pays 50%)
Paying more out of the three guarantees the primary player the right to set his console as primary. This means that he gets to re-download the game anytime he wants and play with any PSN ID.
Hope I've been able to clarify what that was.