Primary Source: Primary sources are firsthand documents that provide direct evidence on your topic. They are most often created during the time the events you are studying occurred. Examples include original documents (diaries, speeches, interviews), creative works (novels, photographs, poetry, music, art works), and relics and artifacts (pottery, textiles, buildings).
Secondary Source: Accounts written after the fact with the benefit of hindsight. They are interpretations and evaluations of primary sources. They are not evidence, but commentary. Examples include magazine / newspaper articles, essays, reviews, commentaries, biographical works, literary criticism.
Tertiary Source: Presents summaries or condensed versions of materials, usually with references back to the primary and/or secondary sources. Examples include textbooks, dictionaries, encyclopedias, and handbooks.
Scholarly: Are written by (and usually for) experts in the field and contains original research. It often (but not always) goes through the peer-review process where other experts in the field look at the work for accuracy and validity. Examples include academic journals.
Popular: are written with a general audience in mind. They are usually to inform, persuade, or entertain. Popular sources help answer who, what, when, and where questions and are essential for finding information about current events or issues. Popular sources range from research-oriented to special interest, agenda-driven publications. Examples include newspapers, magazines, and websites.