When research is conducted, two types of sources are considered for studies - primary and secondary sources. Primary sources are events that are reported firsthand like original artworks or letters from eyewitnesses and so on. They contain raw data.
Secondary sources are discussions or papers or articles, etc written based on analyses done on primary or secondary sources.
The print is a secondary source used for research that contains material/content printed on paper. Articles, books, scholarly journals are all examples of print sources.