Kabbalah -- lit.: received; Jewish mysticism, based primarily on the second century “Zohar,” and on the teachings of the Arizal (16th century, Tzfat). Also refers to someone “accepting” upon himself a spiritual commitment.
karmelit (karmelis) -- a public domain in which less than 600,000 people travel daily. Carrying on Shabbat in these areas and transferring items from private domains into these public ones is prohibited by the rabbis, unless an eruv has been established from before Shabbat
kiddush hachodesh -- decision from the Sanhedrin (Jewish Supreme Court) to accept testimony from witnesses who observed the first sighting of the new moon, thereby determining when the new month should begin
kohen (pl.: kohanim) -- descendent of Aaron (Moses's brother, and the first kohen), today, a kohen gets the first aliyah in shul, and has certain restrictions regarding marriage, visiting a cemetery, etc.