What does the phrase business clothes in paragraph 2 mean?

Câu hỏi :

Instructors at American colleges and universities use many different teaching methods. Some instructors give assignments everyday. They grade homework. Students in their classes have to take many quizzes, a midterm exam, and a final test. Other instructors give only writing assignments. Some teachers always follow a course outline and usually use the text book. Others send students to the library for assignments.