]]1. A straight line intersecting a circle or other curve, or a straight
line connecting the ends of an arc.
2. (symbol c). In aeronautics, a straight line intersecting or touching an airfoil profile at two points; specifically, that part of such a line between two points of intersection.
This line is usually a datum line joining the leading and trailing edges of an airfoil, joining the ends of the mean line of an airfoil profile, from which the ordinates and angles of the airfoil are measured. As such a datum line, it is sometimes called the geometric chord, to distinguish it from a chord established on the basis of any other considerations.
3. = chord length.
In sense 3, points or stations along a chord are designated in percentages or fractions of the chord or chord length from the leading edge, as, a point at 25 percent, or one-quarter, chord.
This article is based on NASA's Dictionary of Technical Terms for Aerospace Use