These have two common uses. One refers to the medical or social standards determining whether a person may or may not be allowed to enter a clinical trial. The criteria usually include age, gender, type and stage of a disease, previous treatment history and other medical conditions. The aims are to identify experimentally appropriate participants and to avoid harming them.
The other relates to the scientific standards set to determine which items in a literature (journal articles, book chapters, etc.) will be included in a systematic review or meta-analysis. The criteria usually include quality and specific tests related to the purposes for which the review is being conducted.