The document discusses the differences between formal and informal language. Formal language is characterized by complex sentences, impersonality, learned vocabulary, and Latin-derived words. Informal language uses simpler grammar, personal evaluation, and colloquial or slang terms. Examples are given of formal versus informal letters, speech, and common word equivalents. Guidelines are provided for avoiding informal language when writing formally, such as not using contractions, first/second person pronouns, or starting sentences with conjunctions. Common colloquial words and expressions are also identified.