It means chaos. It means friendship-ending throws. It means four controllers, one split screen, and no idea whose character is whose.
The "Pair Play" mode is the heart of the four-player experience in the series. In this mode, two teams of two players face off, with each human player controlling one of the two characters on their team. Tekken Tag Tournament (Original): tekken tag tournament 4 player
Why did Namco abandon this brilliant mode? After Tekken Tag Tournament 2 (2012), the series moved strictly to 1v1. It means chaos