a Marxist-Leninist terrorist group of Kurds trying to establish an independent Kurdish state in eastern Turkey

PPK (ППК in Cyrillic letters) was a famous Russian trance duo that was based primarily in Rostov-on-Don. The group consisted of Sergei Pimenov and Alexander Polyakov.

Polizei Pistole Kriminal, notably the Walther PPK as used by James Bond.

Peter Parker, The Spectacular Spider-Man

The distance between the mean and the nearest specification limit divided by (3 x long term standard deviation ).

the performance index