According to google AI Overview, sources are categorized in research and information gathering into three main types based on their proximity to the original event or information: [1]
Primary Sources: Firsthand accounts, raw data, or original documents created at the time of an event (such as diaries, letters, eyewitness interviews, photographs, or official records). [1, 2, 3]
Secondary Sources: Materials that are one or more steps removed from the event, which analyze, interpret, or build upon primary sources (such as biographies, history books, or documentary films). [1, 2]
Tertiary Sources: Compilations that summarize, index, or synthesize secondary and primary sources (such as encyclopedias, dictionaries, and general textbooks). [1, 2]