Exclusion criteria refers to the specific characteristics, conditions, or circumstances that are used to exclude certain individuals or subjects from participating in a research study. These criteria are established by researchers to ensure that the study results are valid and reliable by excluding individuals who may introduce bias or confound the results. Exclusion criteria may include factors such as age, gender, medical history, current health status, medication usage, and other relevant characteristics. By carefully selecting participants based on exclusion criteria, researchers can improve the internal validity of their study and make more accurate conclusions about the effects of the intervention being studied.