Wikipedia:Define and describe

If its subject is amenable to definition, and article should give a concise, conceptually sound definition in its opening sentence and then proceed with a description. If the article is long (more than one page), the remainder of the opening paragraph should summarize[?] it.

To define a concept means, essentially, to make its meaning unambiguous and adequately precise. To do this you must show not only what a concept is, but what it isn't. You must show how the concept relates to other concepts of the same class, thereby establishing the limits of the concept.

The description differs from the definition in that it shows the properties of the concept, rather than how the concept relates to others of the same class. Description without definition is mere anecdote.

For example, an article on fiat money could begin: "Fiat money is money in which the government gets to pick whose face appears on each bill." This is true enough, but it is a rather poor definition, since it fails to show how the concept relates to other concepts of the same class. A conceptually sound definition be: "Fiat money is money issued by a government that has value because that government legally requires people to treat it as having value, rather than because it is backed by specie." One could then elaborate with a description: "Fiat money is said to be backed by the full faith and credit of the issuing government. The value of the money fluctuates with the credibility of the government..., etc."

If a topic is not a concept, then a conceptually sound definition may not be possible. For example, Chester Arthur[?] is not amenable to definition. One can only describe him and his place in history. Care should be made to describe in such a way that the factors likely to be considered important are given precedence.

See debate.