extensional adj 1: defining a word by listing the class of entities to which the word correctly applies
Extensional \Ex*ten"sion*al\, a. Having great extent. [1913 Webster]
extensional Extensional properties, e.g. extensional equality, relate to the "black-box" behaviour of an object, i.e. how its output depends on its input. The opposite is intensional which concerns how the object is implemented.