"Who's Who" is a reference book that provides biographical information about notable individuals in various fields, such as politics, business, science, and the arts. It typically includes details like a person's career, achievements, and contributions, making it a valuable resource for researchers, students, and anyone interested in learning about influential figures. The publication has been produced in various countries and often updates its content annually to reflect changes in people's careers and new entries. It serves as a comprehensive directory, similar to biographical dictionaries or encyclopedias, helping users quickly find information about prominent personalities.