Referring to the Greek prólogos and taking its origin from within the Greek theater regarding a character who would present the setting and context of a play before it begins, and thus, it would be transferred to its common and current use which we see in books as an introduction. Prólogos is formed by the prefix pro-, in this case applied as an antechamber, and logos, for ‘to know’, with roots in the Indo-European *leg-(1), for ‘to gather’.