Ein beit midrash bli chiddush, there is no house of study without innovation, runs a popular saying. Original interpretation is essential to the process of traditional Jewish study.
The proudest achievement of a yeshivah student is to arrive at a chiddush, a new addition to the accumulated knowledge of the generations. Rabbis publish their most treasured insights in books of chiddushim, novellae which present original twists of argument and interpretation.
It may seem surprising that yeshivah study, which places such weight on traditional authority, should also value chiddush, which is a noun form of chadash meaning, simply, new.
Rabbi Joseph Soloveitchik (1903-93) distinguishes between chiddush, innovation within a tradition, and shinui, change which represents a sharp break from tradition. In Rabbi Soloveitchik's view, chiddush is an aspect of imitatio Dei (imitation of God). Through it we become creative partners with God in the unfolding of the Torah's meanings. On the other hand, shinui, which is not deeply rooted in traditional knowledge, risks becoming subjective and arbitrary.
Chiddush is so common a word among speakers of yeshivish (the dialect of English spoken by those who have spent a long time in yeshivah) that it has entered everyday use. In this context, it means something like a surprising discovery or invention, as in "it's a chiddush to me that the JC has column on Jewish words."