Qi (气) is an ancient Chinese concept roughly meaning energy or spirit energy. It is a kind of life force that flows through all beings in the universe. The concept originated in China and spread throughout neighboring countries in Asia.
Pronunciation
In modern Chinese (普通话), it sounds similar to Chi (Chee). However in some other dialects (southern) and Japanese, it sounds more like Ki (Kee).
It is different from the 'chi' in Taiji 太极 ('Tai Chi' in the old spelling).
But it is the same qi as in the Yi Qi Dao league (一气道盟).
Qi is the modern pinyin spelling of the hanzi (气). Modern pinyin is the preferred way to transliterate Chinese nowadays.
Donghua
All Daoists and Yaoguai use Qi to summon magical spells. Wang Fugui uses his life qi / energy to summon his legendary Wangquan Blade. Huandu Qingtian uses up his inert qi to summon powerful poison spells like Venom Body. Wangquan Baye is able to channel the qi used in Qingtian's poison spells with his Wangquan Blade. Bai Yuechu uses qi for his move Qitun Tiandi (Heaven Earth Devour), etc.