In the case of nouns, this is equivalent to specifying the properties that an object needs to have in order to be counted as a referent of the term.
For example, an intensional definition of the word "bachelor" is "unmarried man".
As the name might suggest, this is the type of definition used in Linnaean taxonomy to categorize living things, but is by no means restricted to biology.
Then, we've described the differentia, the specific properties that make it its own sub-type: it has a hemline above the knee.
The terms "intension" and "extension" were introduced before 1911 by Constance Jones[2] and formalized by Rudolf Carnap.