Statistically derived
dose of a chemical or physical agent (radiation) expected to produce a certain effect
in 50% of test organisms in a given population or to produce a half-maximal effect
in a biological system under a defined set of conditions.
Source:
PAC, 1993, 65, 2003
(Glossary for chemists of terms used in toxicology (IUPAC Recommendations 1993))
on page 2068
)