a preliminary discussion; introductory essay, as prefatory matter in a book; a prologue.
2.
Usually, prolegomena.(sometimes used with a singular verb) a treatise serving as a preface or introduction to a book.
Origin: 1645–55; < Neo-Latin < Greek prolegómenon, neuter of passive present participle of prolégein to say beforehand, equivalent to pro-pro-2 + légein to say (akin to lógoslogos)
1652, "learned preamble to a book," from Gk. prolegomenon, neuter passive prp. of prolegein "to say beforehand," from pro- "before" + legein "to speak" (see lecture) + suffix -menos (as in alumnus). The same sense is in preface.