A description consists of an enumeration of the quantitative and qualitative parameters which define something, that is, what something looks like, sounds like, feels like, etc. A complete description includes useful subtle differences which can be useful for distinguishing one thing from another such as DNA information as well as gross characteristics commonly noticed which in popular culture define something such as "a giraffe is an animal with a very long neck".
Rigorous description is created and used in scientific disciplines as technical terminology.
In linguistics (the scientific study of language), prescription and description are often at odds with each other. Descriptivists reject the formation of arbitrary normative rules. Instead, they insist on describing languages as they are used in practice, rather than how they should be used according to some formal orthographical system.