Elephant test
The term elephant test refers to the abilty to recognise something while being unable to describe it. It may be derived from the poem, The Blind Men and the Elephant, by John Godfrey Saxe, which explains how six blind men each have completely different interpretations of what an elephant is like, and the complete description can only be derived by combining their information
In the case of Cadogan Estates Ltd v Morris [1998] EWCA Civ 1671, Lord Justice Stuart-Smith referred, at paragraph 17, to "the well known elephant test. It is difficult to describe, but you know it when you see it."[1]
In a similar vein, U.S. Supreme Court Associate Justice Potter Stewart is famous for a quotation from his opinion in the obscenity case of Jacobellis v. Ohio (1964). Stewart wrote in his short concurrence that "hard-core pornography" was hard to define, but that "I know it when I see it and the motion picture involved in this case is not that."