W xor X

W xor X, commonly written as W^X, is a security policy in some operating systems, such as OpenBSD (and is planned to be implemented in new Linux kernels), in which a page can only be either writable (W) or executable (X), but never both at the same time. This policy is enforced in order to alleviate the problem of buffer overflows and related attacks; by ensuring that the stack is not executable (since it is writable), arbitrary code injected into the stack will not execute but, instead, will cause the program to terminate with a signal.

According to Theo de Raadt, author of OpenBSD, W^X is pronounced "W xor X", or phonetically, "W zor X".