Encyclopedias, dictionaries, handbooks, and Wikipedia are all examples of reference sources.
These sources are good places to start your research. You can find definitions and a brief overview of your topic by consulting a reference book or website.
Doing research on aging? You might want to take a look at AARP Research.
Remember, reference sources are only FYI!
Never cite a reference source in your research paper or project.
You can use a reference source to lead you to other academic sources, however, by finding the citations provided in the References/Bibliography/Works Cited list.