Books: Substantial stand-alone texts. This can include textbooks, books for general audiences, and scholarly books written by and for experts. Scholarly books tend to fall into two categories: single author "monographs" a particular topic and "edited collections" that gather together shorter texts by several different authors on related topics. Scholarly books will usually present an argument about their topic.

Articles: Shorter texts presented within a larger publication, usually a periodical (publication that comes out in a series of issues at regular intervals). Periodicals you might encounter in your research include magazines for general audiences, trade publications for people who work in a particular field, and scholarly or academic journals written by and for academic experts. Scholarly articles usually present an argument about a very specific topic. 

Media Sources: Media sources like newspapers, magazines, and other news coverage may also come up in your research, especially if you're looking for information about recent events. It's important to be aware of the sources of your news coverage, the different types of content included in "news" sources, and any potential bias or conflict of interest in coverage.

Web Sources: Searching for information on the open web, via Google, for example, can be complicated; so much information is available that it can be hard to assess whether you're source is appropriate. Results might include any of the source types above, as well as personal blogs, social media, corporate and government websites, and even web-based scholarly projects. 

Data and Statistics: Information collected through studies and surveys can be presented in its raw, uninterpreted form (data) and in an analyzed form (statistics). While this information can look objective, how data was collected and the ways it's represented can be misleading and should be evaluated carefully.