A definition thought of as getting at what the object defined really is, as opposed to a nominal definition, that merely indicates enough properties to locate it: ‘gold is the element with atomic number 79 (or atomic weight 196.967)’ might be a real definition, as opposed to ‘gold is the yellow, shiny, heavy, valuable stuff of which a lot is kept in Fort Knox’. The distinction is associated with Locke . See also essence.
Philosophy dictionary. Academic. 2011.