The subject content textbooks that you were given or assigned to use in school are typically examples of which type of information source?
Subject content textbooks in math, social studies, history, sciences, English language arts, etc. are typically secondary sources. Primary sources are used in school too; but they are original works, e.g. novels, books of poetry, books of short stories, plays, etc. for English language arts; or firsthand accounts like journals, diaries, letters, news reports or articles, etc. written during the time period studied for history, which you may have been assigned to read in school along with subject textbooks. You probably also used tertiary sources in school, but as references—e.g. encyclopedias, bibliographies, abstracts, etc.