Definitions for "Critical dimension"
Any dimension critical to device performance
the width of a patterned line or the distance between two lines, monitored to maintain device performance consistency; that dimension of a specified geometry that must be within design tolerances. [ASTM F127-84] Also see linewidth.
the width of a line or space that has been identified as critical to the device being fabricated operating properly. Critical dimensions are frequently measured on some or all wafers following any photolithography or etching process in which the dimensions are critical.