Lebesgue Sum
where
is the Measure of the Set 
of points on the 
-axis for which 
.- Lattice Theory
- Latus Rectum
- Laurent Polynomial
- Laurent Series
- Law
- Law of Anomalous Numbers
- Law of Cancellation
- Law of Cosines
- Law of Large Numbers
- Law of Sines
- Law of Small Numbers
- Law of Tangents
- Law of Truly Large Numbers
- Lax-Milgram Theorem
- Lax Pair
- Layer
- Leading Digit Phenomenon
- Leading Order Analysis
- Leaf (Foliation)
- Leaf (Tree)
- Leakage
- Least Bound
- Least Common Multiple
- Least Deficient Number
- Least Period