Books

• long form works offering in-depth research on a topic
• provides a level of analysis across subjects, perspectives, implications, and disciplinary approaches not possible in a shorter publication
• may be popular, i.e. written primarily for a general audience, or monographs, written for and by scholars in a particular field, distributed by a university press; edited monographs or edited anthologies are books that contain a collection of original research articles

Reference

• summaries of facts, definitions, histories; provides basic overviews, factual information, resource recommendations
• recommended for overviews, foundational knowledge and resource recommendations, exp. Oxford Bibliographies Online.
• examples: specialized dictionaries, encyclopedias, yearbooks, bibliographies

Primary Source

• presents new findings, theories, research, or evidence, free from the interpretation of others
• new and original ideas and findings; presents first-hand accounts or observations
• examples: original research articles, datasets, evidence, objects, letters, newspaper articles, diaries

Secondary Source

• describes, reviews, or analyzes works published by other researchers
• provides an overview of current knowledge on a given area, offers deeper interpretation of primary sources
• examples: review articles, popular books and monographs

Popular Source

• materials created for a general audience; publications may or may not undergo editorial review; frequently authored by journalists or researchers 
• presents accessible, easier to understand information; likely to appear earlier in the information timeline
• examples: non-academic books, newspaper and magazine articles, websites and more

Peer-Reviewed

• a source that has been reviewed by experts in a field (i.e., peers) who accept, provide comments and recommendations, or reject the source for publication
• aims to ensure that only high quality research is published by determining the validity, significance and originality of the research and improves the quality of submission
• examples: most if not all original research articles, theoretical articles, and review articles published in scholarly journals

Original Research Article

• article that presents new and original research, ideas, or findings based upon research or analysis conducted by the article's author(s)
• presents the most current research produced on a narrowly defined topic
• also known as empirical research articles, primary source research articles

Theoretical Article  

• criticizes, develops or advances a particular theoretical perspective
• may question dominant assumptions and approaches, or stimulate critical debate

Review Article

• reviews multiple original research articles on a specific topic
• analyzes the current state of research, including major advances and discoveries, ongoing debates, and gaps in knowledge
• offers a strong level of evidence, in particular when following an evidence synthesis protocol
• examples: systematic review, meta-analysis, scoping review; not to be confused with book reviews

Working Paper & Preprint

• preliminary research reports or articles that have not been peer-reviewed; works may be under consideration for publication or under peer-review
• intends to expedite the dissemination of research findings

Grey Literature

• materials published outside of scholarly, peer-reviewed journals; quality standards for grey literature may be less stringent
• qualifies as a primary source if the source reports original research
• may present preliminary research projects (conference proceedings); may represent the primary method of knowledge dissemination outside the academy (reports, policy papers) 
• examples: government or organizational reports, lab notebooks, blogs, pre-prints, conference proceedings, etc

Dissertation/ Thesis

• longer-form work produced by an individual student's research while in a graduate program; the author may develop the project into a published book in the years following graduation
• original research; offers in-depth insight into how the research was conducted and useful for citation mining
• not peer-reviewed but written under the guidance and review of an academic advisor and committee