The term "extra quality" in relation to save data refers to the high-quality save files that contain detailed information about the player's progress. In the case of Tekken 5 on PCSX2, extra quality save data can include detailed character stats, unlocked items, and tournament mode progress. Having access to extra quality save data allows players to enjoy a more seamless gaming experience, with fewer interruptions and more freedom to experiment with different characters and playstyles.