It's always best to get it from the horse's mouth. Information has been filter, manipluated, repackaged, and had evil things done to it.
An original source of information on the topic.
A primary source is usually any item that directly documents the object of your research. Characteristics of primary sources include: items created by participants in the object of research and/or items created during the same timeperiod of object of research. In this regard primary sources are often (though not always) subjective accounts of events, people's lives and opinions, phenomena, occurrences, etc. (expand and revise)
A secondary source is usually any item that analyzes the object of your research. (expand and revise)
What is the deal with them... crazy encyclopedias.
So what are you researching? An event? A person's life and work? Perhaps a disease or natural phenomenon? A location or a business?