Prescriptive (definition)

this is a term used to describe a set of rules which are used to describe grammar and aim to describe the correct usage of grammar in a language. These rules are usually formed due to purity, logic, and historical or literary excellence. These rules are set due to the culture at the time. An example of this would be whether or not to use “who” or “whom” in English.

Reference

Crystal, David. A Dictionary of Linguistics and Phonetics. The language library. Oxford, UK: Blackwell, 1997.