Gadol or godol גדול (plural: gedolim גדולים) (Hebrew "big" or "great"), is a Hebrew term used by Haredi Litvish Jews to refer to the most revered rabbis of their generation. These rabbis are usually held in high esteem by other Haredi or Orthodox Jews, though not necessarily to the same degree as by Litvish Jews. The term is almost exclusively used to refer to rabbinic leaders since World War I. Earlier major rabbis are given other titles, such as Rishonim or Achronim.
The term 'Gadol' is also used by Orthodox and other Haredi Jews, though they do not have the same concept of "The Gedolim".
The term gadol hador refers to the "great/est (one of) the generation" denoting one rabbi who is presumed to be even greater than the others. Other variations of the term are Gadol Yisrael or a Gadol BeYisrael (plural: Gedolei Yisrael), meaning "great one of the Jewish people". A similar title is Rashkebahag, which is an acronym for "Rabbon shel kol bnei hagolah" (The sage and teacher of the entire Jewish diaspora). Another term is Manhig Yisroel (plural: Manhigei Yisroel), literally "leader of Israel". The title gadol hador is usually only given to one Jewish Sage at a time, while the title "Rashkebahag" can be given to a few, and the term Gedolei Yisrael collectively refers to all leading rabbis in the Haredi community.
Most often a gadol functions as a rosh yeshiva (the head of a yeshiva Talmudical school), and can be a Hasidic Rebbe. A gadol is quite often also a posek (a decisor of Halakha - Jewish law) and may be the author of rabbinic literature and responsa. Adherents of Torah Judaism often presume that a gadol has some degree of ruach hakodesh ("divine spirit"); the gadol's teachings and statements therefore become the crux of Daas Torah.
Read more about Gadol: Hebrew Usage, Partial List