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In algebraic geometry, a chordal variety of a variety is the union of all the chords (lines meeting 2 points), including the limiting cases of tangent lines.

References

Griffiths, Phillip; Harris, Joseph (1994), Principles of algebraic geometry, Wiley Classics Library, New York: John Wiley & Sons, ISBN 978-0-471-05059-9, MR 1288523