DICTION
Diction is the choice of language used by the speaker or writer. For instance a young adult uses different words, language, style depending on to whom s/he is speaking or writing. Students use a "diction" in class, at home, at work, with friends. Here is a link to a good site that provides good examples.
Example:
Simple initial salutations may illustrate this:
Yo, Hello, Howdy, Hi, Hey are examples of diction and which word you would choose when meeting someone.