Sources are any place you obtain information, data, or facts. Sources include the following:
Peer review is the evaluation prior to publication of scientific, academic, or professional work by others working in the same field.
Primary sources are contemporary accounts of an event, written by someone who experienced or witnessed that event. Some examples include eyewitness accounts, statistical data, legal documents, and video or audio footage.
Secondary sources are interpretations and evaluations of primary sources. Secondary sources are not evidence, but rather they are commentary on and discussion about evidence. Some examples include newspaper and magazine articles, reviews of books or movies, and journal articles that discuss another person's work.
Ithaca Library has an excellent website about the differences between primary and secondary sources.