Intension and Extension

To give an “intensional definition” is to define a word or phrase in terms of other words, as a dictionary does. To give an “extensional definition” is to point to examples, as adults do when teaching children. The preceding sentence gives an intensional definition of “extensional definition”, which makes it an extensional example of “intensional definition”.

Source: http://lesswrong.com/lw/nh/extensions_and_intensions/