this is CODE!!!! (1)

Binary;

$X = 1$

$O = 0$

Let the letters of the alphabet equal their numerical equivalent (ie. A = 1, B = 2, C = 3, ... Y = 25, Z = 26). The examples provided abide by this encoding rule.

So, to get the answer simply convert 26 (Z) into binary and re-encode with Os and Xs.

hint: binary