The capital Greek letter (capital chi) is visually very similar to the uppercase Latin letter X. For that reason, refer to the usage of Capital X for how the symbol appears in math.
Symbol  Format  Data 

Χ  Unicode 

TeX 


SVG 
The Greek Alphabet is used throughout math to represent variables, constants, and coeffecients within math expressions, formulas, and equations.
The Greek letter χ (chi).