In the Orthodox Jewish community a Kollel is effectively an institute for advanced Talmudic study. In the non-Orthodox Jewish community a kollel or adult-ed center has courses available on Talmud, Midrash, learning Hebrew, Jewish ethics and related topics; less emphasis is given to Talmud.
A great champion for Kollelim (plural) was Rabbi Aharon Kotler, the founder of Beis Medrash Govoha, a Yeshiva in Lakewood.
Most Orthodox Jewish Yeshiva students study in Kollel for a year or two after they get married. living off of donations, charity or the salaries of their wives and in-laws. In the Israeli Ultra-Orthodox Jewish community many hundreds of men study full-time in a Kollel for many years, living on welfare and donations. This has been known at times to cause a great deal of resentment from the Israeli public at large, garnering criticism from the Modern Orthodox, non-Orthodox and secular Jewish community.