An ostensive definition conveys the meaning of a term by pointing out examples.
This type of definition is often used where the term is difficult to define verbally, either because the words will not be understood (as with children and new speakers of a language) or because of the nature of the term (such as colors or sensations).
An ostensive definition assumes the questioner has sufficient understanding to recognize the type of information being given.
Thus if I know that someone means to explain a colour-word to me the ostensive definition "That is called 'sepia' " will help me to understand the word.... One has already to know (or be able to do) something in order to be capable of asking a thing's name.
[2] John Passmore states that the term was first defined by the British logician William Ernest Johnson (1858–1931): "His neologisms, as rarely happens, have won wide acceptance: such phrases as "ostensive definition", such contrasts as those between ... "determinates" and "determinables", "continuants" and "occurrents", are now familiar in philosophical literature" (Passmore 1966, p. 344).