chi is a chinese word, roughly meaning "life energy"
or
chi is the 22nd letter of the Greek alphabet. The lower-case letter χ is used as the symbol for the Chi-square distribution or Chi-square test in statistics.
SkeptischeEcke: Chi Kung (Qi Gong)
Su Tzu's Chinese Philosophy Page
Skeptical Inquirer:China, Chi, and Chicanery
Tai-Chi-Arbeitskreise Taoistische Philosophie in Theorie und Praxis