This document discusses the differences between formal and informal English, including idioms, slang, euphemisms, and metaphors. It provides tables that define key terms for each category. Formal English is used for academic writing and speeches, follows standard conventions, and uses precise vocabulary. Informal English is used for everyday conversations, may violate standard rules, and incorporates contractions, slang, and familiar terms. Idioms usually have fixed meanings and cannot be literally translated, while slang terms are non-standard and specific to a group. Euphemisms substitute indirect terms for taboo concepts, and metaphors use figurative language to describe something in terms of something else.