"Reference sources" can provide helpful background information about a topic and include sources such as encyclopedias, topic overviews, dictionaries, timelines, and bibliographies.
Online resources such as Wikipedia can be a great start, but usually will not be considered reliable. The following databases have background information from credible sources which you can use and cite in your academic assignments.
Keywords for Environmental Studies by 
A Dictionary of Environment and Conservation (3rd ed.) by Search over 600 full text reference books for your topic. It also has article links to library databases (such as ProQuest and EBSCO).
Includes language and subject dictionaries, general reference books, subject-specific reference books, timelines, quotations, and overview pages.
Additional reference databases can be found in A-Z Databases by limiting database type to Reference.