The latus rectum of a conic section is the chord through a focus parallel to the conic section directrix (Coxeter 1969). "Latus rectum" is a compound of the Latin latus, meaning "side," and rectum, meaning "straight."

Half the latus rectum is called the semilatus rectum.

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Weisstein, Eric W. "Latus Rectum." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/LatusRectum.html