Lambda (unit)
Lambda is a non-SI unit of volume equal to 10−9 m3, 1 cubic millimetre or 1 microlitre. Introduced by the BIPM in 1880, the lambda has been used in chemistry and in law for measuring volume, but its use is not recommended.
This use of λ parallels the pre-SI use of μ on its own for a micrometre and γ for a microgram. Although the use of λ is deprecated, some clinical laboratories continue to use it. The standard abbreviation μL for a microlitre has the disadvantage that it can be misread as mL. In pharmaceutical use, no abbreviation for a microlitre is considered safe. The recommended practice is to write "microlitre" in full.
