Non-SI unit of volume, L = 10E-3 m^3. The other allowed symbol is l.
Source:
Green Book, 2nd ed., p. 111 (https://goldbook.iupac.org/files/pdf/green_book_2ed.pdf)
See also:
PAC, 1986, 58, 1405. 'Recommendations for the presentation of thermodynamic and related data in biology (Recommendations 1985)' on page 1407 (https://doi.org/10.1351/pac198658101405)
PAC, 1996, 68, 957. 'Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)' on page 979 (https://doi.org/10.1351/pac199668040957)