x axis. [JP 1-02] (DoD) A horizontal axis in a system of rectangular coordinates; that line on which distances to the right or left (east or west) of the reference line are marked, especially on a map, chart, or graph.
X.400 Interpersonal Message System (IPMS). International civilian standard for e-mail messaging - the P22 content type. This is the content type used in virtually all vendor supplied e-mail packages, that the primary content type used in e-mail communications on the Internet. Of the 93 Elements of Service in the P22 Content Type, only 21 are mandatory for support by all applications. Of the remaining 72 optional Elements of Service there is no requirement for vendors to implement them, though some are needed to satisfy DMS requirements. The result is that of the array of commercial products on the market that implement X.400 P22, full interoperability is largely non-existent. Implementation of content type P772 in the Defense Messaging System remedies this deficiency.
X-scale. [JP 1-02] (DoD, NATO) On an oblique photograph, the scale along a line parallel to the true horizon.