Bioactivity is the inherent property of a substance, material, or stimulus to elicit a measurable effect on a biological system. As a central concept and research area across disciplines like pharmacology, toxicology, biochemistry, and materials science, it encompasses the investigation of the qualitative and quantitative nature of these biological responses, including dose-response relationships, specificity, and underlying mechanisms, which is crucial for assessing therapeutic potential, toxicity, environmental impact, and designing novel biologically active agents or materials.