"Because it is in its original form, the information in primary sources has reached us from its creators without going through any filter. We get it firsthand" (Ohio State University Libraries).
"These sources are translated, repackaged, restated, analyzed, or interpreted original information that is a primary source. Thus, the information comes to us secondhand, or through at least one filter" (Ohio State University Libraries).
"These sources further repackage the original information because they index, condense, or summarize the original.
"Typically, by the time tertiary sources are developed, there have been many secondary sources prepared on their subjects, and you can think of tertiary sources as information that comes to us “third-hand.” Tertiary sources are usually publications that you are not intended to read from cover to cover but to dip in and out of for the information you need. You can think of them as a good place for background information to start your research..." (Ohio State University Libraries).
Learn the differences between primary, secondary, and tertiary sources in the following video.