Countably Infinite Set
Any Set which can be put in a One-to-One correspondence with the Natural Numbers(or Integers), and so has Cardinal Number 
. Examples of countable sets include theGeorg Cantor 
showed thatthe number of Real Numbers is rigorously larger than a countably infinite set, and the postulatethat this number, the ``Continuum,'' is equal to Aleph-1 is called the ContinuumHypothesis.
- Length Distribution Function
- Length (Number)
- Length (Partial Order)
- Length (Size)
- Lengyel's Constant
- Lens
- Lens Space
- Lenstra Elliptic Curve Method
- Leonardo's Paradox
- Leptokurtic
- Lerch's Theorem
- Lerch Transcendent
- Less
- L-Estimate
- Letter-Value Display
- Leudesdorf Theorem
- Level Curve
- Level Set
- Level Surface
- Leviathan Number
- Levi-Civita Density
- Levi-Civita Symbol
- Levi-Civita Tensor
- Levine-O'Sullivan Greedy Algorithm
- Levine-O'Sullivan Sequence