The term "threshold level" refers to the minimum point at which a certain effect or response begins to occur. In various fields, such as psychology and biology, it indicates the level at which stimuli can be detected or a reaction is triggered. For example, in psychology, it might describe the smallest amount of a stimulus needed for a person to notice it. In environmental science, the threshold level can denote the concentration of a pollutant that must be reached before it starts to have harmful effects on ecosystems. Understanding these levels is crucial for setting safety standards and protecting both human health and the environment.