inhibitory concentration (IC)

https://dx.doi.org/10.1351/goldbook.I03036
Concentration of a substance that causes a defined inhibition of a given system: IC 50 is the median concentration that causes 50% inhibition.
Source:
PAC, 1993, 65, 2003 (Glossary for chemists of terms used in toxicology (IUPAC Recommendations 1993)) on page 2060