Most of these resources link to reference sources of some sort.
Reference Sources summarize a topic. They tell you basic things, like when and where an event happened, a simple or introductory description of an idea or theory, or the most important points about a person's life.
Reference sources generally do not offer analysis, and if writing about a controversial issue, will usually remain neutral.
Reference sources are useful for choosing a topic to write about, and for learning enough about a topic to allow you to find and understand more detailed sources like books or journal articles. They can lead you to more detailed or interesting sources.
Because they summarize the information found in other sources, add no new analysis or ideas, and intentionally avoid going into too much detail or making an argument, however, they are not good sources to cite in a research paper.
