, the broadest definition of a rebbe is merely that of a Jewish teacher
. For Hasidim
this gets considerably more involved, as the teacher becomes more of a mystic guide
in matters of spirituality
. A distinction is sometimes made between the two by making Rebbe a proper noun in the case of the latter and leaving it uncapitalized in the general case, but this isn't applied equally by all writers.
Rebbes and rabbis are not the same; rabbis are scholars (and students) of Jewish law respected for their intellectual, learned and interpreted approaches while a rebbe is a saintly spiritual master who intuits and meditates on matters pertaining to the soul, reincarnation and other such more-metaphysical matters. It is not required for a rebbe to be an ordained rabbi, nor for a rabbi to be a rebbe, athough there are occasional instances of one person adopting both callings. This-all is often muddled on account of "Rebbe" sometimes being translated as "Grand Rabbi" but that is not a term in use by Hasidim.
Every Hasidic sect focuses on the teachings of a particular Rebbe and is usually named after the Rebbes' hometown, even if (in 99% of the cases since the Holocaust) the Hasidim no longer live there.
Two polar opinions on the nature of being a rebbe are espoused by the Lubovich group and the Breslov Hasidim.
* Lubovitchers believe that a Rebbe is a wholly separate category of person from ordinary folk, intrinsically born a Rebbe and possessive of a soul with innately holier properties than the rest of us. This belief goes to the extent of many Lubovichers believing their late Rebbe Menachem M. Schneerson to have been a candidate for the Messiah.
* Taking the other extreme, the Breslover Hasidim follow the teachings of their Rebbe Nachman of Breslov in believing that a Rebbe starts out the same as any of us and attains the higher spiritual levels of a Rebbe through his own efforts.
It should be noted that between these two extremes, there are as many variations of opinions about the nature of a Hasidic Rebbe as there are sects, but most of them fall on a continuum between the two above stances.
To gentiles, a Hasidic Rebbe may be best understood as roughly analagous to the abbot
of a monastery or a Hindu guru
, in that he is the spiritual guide for a group of disciples, in a community a living example of how to live as a Jew.