Discourse analysis is the study of written and spoken language use beyond the sentence level. It examines how language is used in a social context and how it relates to other factors like culture. There are different types of discourse including narrative, descriptive, persuasive, argumentative, and expository. Oral discourse involves spoken communication while written discourse conveys meaning through written language. Some key differences between oral and written discourse are that oral discourse allows for nonverbal cues and can be more spontaneous while written discourse provides more structure and cannot be changed once published.