Orthodox Jews use the term to denote someone that their perceive not only as the religious leader of their congregation, but as their spiritual advisor and mentor. A rebbe is someone whose views are accepted not just on issues of religious dogma and practice, but in all arenas of life, such as politics and social and issues.
One example is Orthodox Hasidic Rabbi Menachem Schneerson, the last leader of the Chabad Lubavitch hasidim; he was referred to as "The Rebbe" bu Lubavitch Hasidim. Each Hasidic sect refers to their leader as "The Rebbe".
Some Hasidic rebbes have thousands of followers, or disciples called hasidim, (meaning "righteous ones"), whilst others may have only a few hundred. Some only have a title , but don't have a following beyond their own family members.