The concentration that cuts a biological process in half — used to measure how potent an inhibitor is.Lower IC50 = more potent inhibitor. Used to characterize inhibitors of enzymes, receptors, or signaling pathways. Complement to EC50, which characterizes agonist potency. IC50 values are assay-condition-dependent — the same compound can show different IC50 values in different assay systems, which is why comparing IC50 values across different studies requires caution.