A secondary source is a work that interprets, analyzes, or comments on primary sources, which are original, first-hand accounts or direct evidence about a topic or event. Secondary sources are one step removed from primary sources and often use them to provide context, explanation, or evaluation. They may summarize, critique, or synthesize information originally presented elsewhere rather than presenting new, original data or firsthand experience

. Examples of secondary sources include:

• Books and scholarly articles that discuss or analyze a topic
• Textbooks that explain scientific concepts without original research
• Documentaries that interpret historical events
• Reviews, biographies, and dissertations
• Encyclopedias and dictionaries
• Newspaper editorials or opinion pieces (depending on context)

The classification of a source as primary or secondary can depend on the research context and how the source is used. For instance, a textbook is generally a secondary source in scientific fields but could be a primary source if studying the history of education

. In summary, secondary sources provide interpretation, analysis, or commentary on primary sources rather than original, firsthand information