A capital Greek letter commonly used to represent eigenvalues, Lagrangians, or parameter sets in mathematics and physics.
Examples
Eigenvalue notation in linear algebra
\Lambda = \text{diag}(\lambda_1, \lambda_2, \ldots, \lambda_n)
Lambda calculus function definition
f = \Lambda x.(x^2 + 2x)
Exterior algebra notation
\Lambda^k V = \text{span}\{v_1 \wedge v_2 \wedge \cdots \wedge v_k\}