Referred to as X-Axis and X Axis; An imaginary line passing left-to-right through the center of the plan view. The left-right direction on the diagram sheet is when it is held in the position to read the text. This imaginary line is used for referance point in both 2D and 3D drawings/drafting.
Found on http://www.quadrasol.co.uk/glossary.php
The horizontal axis in a chart. It displays the range of values possible for the independent variable to take. In time series data, the x-axis represents time. Found on http://www.encyclo.co.uk/local/20140
Usually, the axis in the plane of the laminate used as 0° reference. Typically, the y-axis is the axis in the plane of the laminate perpendicular to the x-axis, and the z-axis is the reference axis normal to the laminate plane in the composite laminate. (See also laminate coordinate axes, off-axis laminate and principal axis.)
Found on http://www.komprex.com/Glossary/index.htm