The Chi-Rho (pronounced "KEE-roe") is a Christian symbol consisting of the intersection of the capital Greek letters Chi (Χ) and Rho (Ρ), which are the first two letters of "Christ" in Greek (ΧΡΙΣΤΟΣ, Christos). The Chi-Rho can represent either Christ or Christianity and is also known as a Christogram.
(from http://www.religionfacts.com/christianity/symbols/chi_rho.htm)
