[m., generally not used in pl.]; morality, ethics; reproof or punishment; a moral movement, based on the study of traditional ethical literature.
Probably the classic text in “Mussar” is “Pirkei Avot”, Ethics of the Fathers.
Some ideas of Mussar are the awesome potential of man to obtain the greatest spiritual heights, serene acceptance of whatever G-d causes to happen to one in life; not over-concern with matters of “Olam HaZeh,” “This World;” preferred is focus on “Olam HaBa,” the “World-to-Come”
Some luminaries of the Mussar school within Judaism were Rav Yisroel Salanter, Rav Eliezer Papo, Rav Yerucham Levovitz and Rav Yechiel Yaakov Weinberg.
In the sense of reproof, the word is used in the context of “mussar ha-neviim,” the warning or reproof of the prophets.
In the sense of punishment, the word is used in the context of “mussar HaShem,” “the punishment of HaShem.”