There are different types of diction used when addressing different audiences. Formal diction is used for highly educated audiences in documents like sermons and journals. Informal diction, including slang, is used for familiar audiences and has a more conversational purpose as seen in emails, letters, novels, and sports broadcasts. Colloquial diction is characteristic of spoken language and writing seeking a conversational effect, while slang uses non-standard terms for humor, irreverence or other effects, especially in casual speech among a group.

1. TYPES OF DICTION
AP Language

2.  Used when addressing a
highly educated audience. This
includes sermons, scholarly
journals, etc.
FORMAL

3.  used when addressing a familiar
or specific audience. This includes
personal letters, emails, and
documents with conversational or
entertaining purposes. This level
also includes "slang" language,
which may be used to create a
specific "flavor" as in sports casting
or novels.
INFORMAL

4.  1. Characteristic of or
appropriate to the spoken
language or to writing that seeks
the effect of speech; informal.
 2. Relating to conversation;
conversational.
COLLOQUIAL

5. SLANG
 1. A kind of language occurring
chiefly in casual and playful speech,
made up typically of short-lived
coinages and figures of speech that
are deliberately used in place of
standard terms for added raciness,
humor, irreverence, or other effect.
 2. Language peculiar to a group;
argot or jargon: thieves' slang.