introductory
adjective
serving as an introduction to a subject or topic; basic or preliminary:
紹介の; 序論の, 前置きの〈章･発言など〉; 入門の〈クラスなど〉.
e.g. an introductory course in Russian.
intended to persuade someone to purchase something for the first time:
初売り(限定)の〈価格など〉
e.g. we are making a special introductory offer of a reduced subscription.
ORIGIN
late Middle English (as a noun denoting an introductory text): from late Latin introductorius, from Latin introducere (see introduce).