There is a term in the science of logic about every definition and explanation: " every definition or explanation of a subject should be inclusive and exclusive". It means that the explanation should be included everything about the subject and excluded unrelated things. In my opinion, this statement also applies for essay. Every essay should cover all aspects of the subject and also should not include irrelevant topics. Therefore above definition can determine the quality and quantity of an assay. Sometimes, only one paragraph describe the subjects and sometimes a multi page report can not explain the subject totally. The purpose of writing assay is also important. Like short story vs. novel; in the short story, you should consider your story with few words but in the novel, reader is expecting comprehensive details.