Cantor's Theorem
The Cardinal Number of any set is lower than the Cardinal Number of the set of all its subsets. A Corollary is that there is no highest 
(Aleph).
- Jensen's Formula
- Jensen's Inequality
- Jerabek's Hyperbola
- Jerk
- j-Function
- Jinc Function
- j-Invariant
- Jitter
- Joachimsthal's Equation
- Johnson Circle
- Johnson's Equation
- Johnson Solid
- Johnson's Theorem
- Join (Graph)
- Join (Spaces)
- Joint Distribution Function
- Joint Probability Density Function
- Joint Theorem
- Jonah Formula
- Jones Polynomial
- Jonquière's Function
- Jordan Algebra
- Jordan Curve
- Jordan Curve Theorem
- Jordan Decomposition Theorem