Providing background information. These sources answer who, what, where, when and why questions and are more useful for purposes of identification than for in-depth research
Providing in-depth and/or historical analysis of a subject
Written by experts in the field. Journal articles are typically published after undergoing a peer-review process. Peer review involves the assessment of the validity, quality, and originality of articles by experts in the same field. These articles present original research data and findings or express a position on a significant question within the field.
Collection of one or more types of materials mentioned above.
Immediate, first-hand accounts of a topic or original source of information about the topic such as diary, manuscript, autobiographic etc.
Created by someone who did not experience first-hand or participate in the events or a topic.
The best research uses everything, all the tools, and the best tool for the task. But not all tools are equal. Google and Wikipedia have their uses, but when it comes to scholarly research, rely on restricted tools/resources which are superior, have more content, and are free to Cornellians.