There are three types of definitions important in scientific work: (a) nominal definition, which states that we agree to use these particular words to describe some phenomenon; (b) operational definition, which asserts the specific measurements one will use to define a concept; and (c) real definition, which attempts to get at the essence of a phenomenon. Real definitions relate a term that has some shared social meaning to its definition. They assert a proposition and thus can be tested empirically. They have truth value and can be a part of a logical system of inferences.
The precise determination of limits, especially of a disease process.