The phrase "primary text" refers to the main or original source of information. It is the primary or most important written material that provides knowledge or facts about a particular subject. Full definition
Many teachers are already using open source content to supplement primary texts. (edutopia.org)
It's really important that in science and history classes, students have access to important primary texts and that they be able to figure out what the speaker is trying to say. (hechingerreport.org)
Students are required to cite primary texts to debate their ideas. (ascd.org)