P.O.K. stands for Podosfairikes Omades Kentrou(Ποδοσφαιρικές Ομάδες Κέντρου), which is Greek for Central Football Teams, meaning the football teams of Athens. The term comes from an event that took place in 1927, when Olympiacos, Panathinaikos and AEK Athens chose to abstain from the Greek Championship after disagreements with the Hellenic Football Federation. The main reason had to do with the Championship's financial status. HFF decided that the league's revenues would be equally divided between all teams that participated, however Olympiacos, Panathinaikos and AEK denied to do so. Later they decided to form a group called P.O.K.' and during that season they played friendly games with each other, since HFF had erased them.
Even though P.O.K. does not technically exist anymore, the name is often used due to the continuing dominance of the three "former P.O.K." clubs in the National A Division. It is an extremely rare occurrence for a team outside the former P.O.K. clubs to finish in the top three of the Championship and when that happens it is said that that team "broke the P.O.K.". Since 1928, only 3 other teams (Aris, AE Larissa and PAOK) have managed to conquer the Greek Championship. PAOK is the team that has managed to break the P.O.K. the most times, and also the last to accomplish it, having finished 2nd for the 2008/09 season, leaving Panathinaikos and AEK in third and fourth place.