1. Criterion or objective by which the successful completion of an activity, program, or project is determined. In a cleanup or decontamination exercise, for example, the endpoint is that level of decontamination at which further cleanup is deemed unnecessary.
2. Final stage of a process at which an effect manifests or is observed. The term 'biological endpoint,' for example, is used for indicating the health effect(s) of an exposure to an hazardous substance.