All languages have different varieties that speakers use in different situations, and some varieties are more appropriate than others, depending upon the occasion. A language variety is basically the style of language that a speaker chooses, whether it be slang, jargon, formal or baby-talk. Social factors are the primary reason that speakers choose different styles.
The physical environment of a conversation or oral presentation plays a large role in the variety of language an individual uses. The difference between sitting in the office of the president of a company and sitting on a recliner at a friend's house watching a football game is tremendous. A speaker's language style reflects these differences in location. Respect and formal speech are used in business settings; however, language is much more relaxed when a person is kicking back with friends.
When a person is talking to another person that he has known for many years, the style of language he uses is quite different from what it would be with a person he just recently met. A person who was just introduced to another would never use unfamiliar jargon or swear. Similarly, age differences are a social factor in speakers' relationships. People use different language styles when conversing with those much younger, similarly aged and older.
The social role of each conversation participant also plays a part in the variety of language used. Interactions between a student and teacher, a pastor and parishioner, and a congressman and fundraiser are much more formal than the language interactions between two socially like-positioned participants. In other words, a student talking to a peer uses a more laid-back style of language than she would when talking to a teacher.
Conversation Topic or Goal
The topic of a conversation and/or its intended outcome are also social factors in the style of language used. Even if two individuals are similar in age, have similar social roles, know each other well and are in a comfortable setting, when the topic of conversation is a serious one, or if one of the participants has a specific goal, the language used is more polite and respectful.