Lambda (upper case Λ, lower case λ) is the 11th letter of the Greek alphabet. In the system of Greek numerals it has a value of 30.

In art and photography, a lambda-print is a positive image, usually a photograph, executed on photographic (light-sensitive) paper using a dedicated laser printer (e. g. Durst Lambda or Océ LightJet), - Durst AG Italy were the first company to develop this digital imaging technology way back in 1995 - as opposed to a C-type or an inkjet print. Thus the phrase lambda print has entered the vocabulary. Tha Lambda was named so due to it being the unit of light wavelengh.

Upper-case letter Λ

• The lambda particles in particle physics
  
• The set of logical axioms in the axiomatic method of logical deduction in first-order logic
  
• The cosmological constant
  

Lower-case letter λ

• A unit of measure of volume (symbol λ) equal to one microlitre (1 μL) or one cubic millimetre (1 mm³)
  
• The wavelength of a wave in physics
  
• The Half-life of a radioactive element in physics.
  
• The radioactive decay constant
  
• The lambda phage virus in biology
  
• Eigenvalues in linear algebra
  
• Function expressions in lambda calculus and, by extension, some programming languages
  
• The language Unlambda is a functional programming language based upon combinatory logic, a simplification of the lambda calculus that does not involve the lambda at all, hence the un- prefix.
  
• Gay pride (explanations for this usage vary) and as a gay signifier, such as the Lambda Literary Award
  
• The Half-Life computer game
  
• stoichiometric fuel to air ratio oxygen sensor in an internal combustion engine's exhaust gas
  
• A Japanese rocket type, Lambda (rocket)
  
• A shuttle type in Star Wars, Lambda Shuttle.
  
• Spartans Painted the Lambda symbol upon their shields; a feared sight of the ancient world was a wall of shields painted with the lambda.