In Yiddish (from which the word has migrated into American English), mensch roughly means "a good person." A role model. A "mensch" is a particularly good person, like "a stand-up guy," a person with the qualities one would hope for in a dear friend or trusted colleague. According to author and Yiddish popularist Leo Rosten,
[A] mensch is a someone to admire and emulate, someone of noble character. The key to being "a real mensch" is nothing less than character, rectitude, dignity, a sense of what is right, responsible, decorous. (Rosten, Leo. 1968. The Joys of Yiddish. New York: Pocket Books. 237)
My last year's New (Jewish) Year resolution was to read "The Book of Jewish Values - A day-by-day guide to ethical living" by rabbi Telushkin. Joseph Telushkin is a Modern Orthodox rabbi whose focus is on ethics. He has published quite a number of books and I quite liked this one in so far that it really was/is a book to live by. I plan to read it again on a daily basis in a year or two.
I enjoyed it so much that I then purchased "A Code of Jewish Ethics", by rabbi Telushkin again. In this books, he develops some of the ideas he tackled in "The Book of Jewish Values", underlining how ethics are part and parcel of Judaism. The more I read it the more it challenged me and made me think of my interactions with the people around me.