Paradox
A statement which appears self-contradictory or contrary to expectations, also known as an Antinomy. Bertrand Russell 
classified known logical paradoxes into seven categories.
Ball and Coxeter (1987) give several examples of geometrical paradoxes.
See also Allais Paradox, Aristotle's Wheel Paradox, Arrow's Paradox, Banach-Tarski Paradox,Barber Paradox, Bernoulli's Paradox, Berry Paradox, Bertrand's Paradox, Cantor'sParadox, Coastline Paradox, Coin Paradox, Elevator Paradox, Epimenides Paradox,Eubulides Paradox, Grelling's Paradox, Hausdorff Paradox, Hempel's Paradox, HeterologicalParadox, Leonardo's Paradox, Liar's Paradox, Logical Paradox, Potato Paradox, Richard'sParadox, Russell's Paradox, Saint Petersburg Paradox, Siegel's Paradox, Simpson's Paradox,Skolem Paradox, Smarandache Paradox,Socrates' Paradox, Sorites Paradox, Thomson Lamp Paradox, UnexpectedHanging Paradox, Zeeman's Paradox, Zeno's Paradoxes
References
Ball, W. W. R. and Coxeter, H. S. M. Mathematical Recreations and Essays, 13th ed. New York: Dover, pp. 84-86, 1987. Bunch, B. Mathematical Fallacies and Paradoxes. New York: Dover, 1982. Carnap, R. Introduction to Symbolic Logic and Its Applications. New York: Dover, 1958. Curry, H. B. Foundations of Mathematical Logic. New York: Dover, 1977. Kasner, E. and Newman, J. R. ``Paradox Lost and Paradox Regained.'' In Mathematics and the Imagination. Redmond, WA: Tempus Books, pp. 193-222, 1989. Northrop, E. P. Riddles in Mathematics: A Book of Paradoxes. Princeton, NJ: Van Nostrand, 1944. O'Beirne, T. H. Puzzles and Paradoxes. New York: Oxford University Press, 1965. Quine, W. V. ``Paradox.'' Sci. Amer. 206, 84-96, Apr. 1962.
- Knapsack Problem
- Kneser-Sommerfeld Formula
- Knights of the Round Table
- Knights Problem
- Knight's Tour
- Knot
- Knot Complement
- Knot Curve
- Knot Determinant
- Knot Diagram
- Knot Exterior
- Knot Linking
- Knot Polynomial
- Knot Problem
- Knot Shadow
- Knot Sum
- Knot Theory
- Knot Vector
- Knödel Numbers
- Kochansky's Approximation
- Koch Antisnowflake
- Koch Island
- Koch Snowflake
- Koebe Function
- Koebe's Constant