Primary

Primary sources are videos, writing, etc. created by or with individuals who can provide eye-witness or first-hand accounts of events or information.

• Examples- Diaries, recordings (audio or video), photos, interviews with witnesses, scholarly articles written by researchers detailing their evidence, meeting minutes, statistics, original documents, transcripts, etc.
• Benefit- Direct transmission of information without external interpretation/misinterpretation
• Concern- Limited perspective, inherent bias, readers without expertise may struggle to correctly interpret and contextualize the source

Secondary

Secondary sources build on primary sources and often incorporate multiple primary sources to provide context or analysis.

• Examples- Second-hand news reports, popular and scholarly books that analyze and contextualize primary sources, biographies, commentaries, scholarly articles that discuss, review, or analyze evidence of others, data visualizations, etc. 
• Benefit- Secondary sources can combine primary sources for a more complete understand of events or topics, offering analysis or context.
• Concern- Secondary sources are inevitably influenced by the perspectives of those who are analyzing and contextualizing so it is important to be aware of their purpose.

Tertiary

Tertiary sources combine information from multiple primary and/or secondary sources to present consolidated summaries  of subjects for ease of access. Sometimes called reference sources or background sources.

• Examples- Textbooks, encyclopedias, handbooks, manuals, factbooks, almanacs, etc.
• Benefit- Excellent starting points for new topics. Efficiently organized, and often indexed collections with valuable vocabulary and topic overviews. Usually provide lists of references allowing readers to backtrack to primary sources. Reliable tertiary sources provided balanced or objective perspectives. 
• Concerns- Tertiary sources are well removed from the original source and may have multiple layers of interpretation embedded.