X0 may refer to: SpaceShipOne flight 15P, the 2004 first privately funded human spaceflight X/0, a notation for the division by zero Turner syndrome, a disorder in which all or part of an X chromosome is absent X0 sex-determination system, as found in some insects X0, heterogametic male designation under this system X0, a smaller rigged version of an X1 (dinghy) X0, running number for N700 Series Shinkansen prototype from 2014 to 2021 X0, zero-level projection or head in linguistics See also XO (disambiguation) X00, a popular DOS-based FOSSIL driver which was commonly used in the mid 1980s to the late 1990s