The Hebrew term lashon hara (or loshon hora) (Hebrew לשון הרע; "evil tongue") is the halakhic term for derogatory speech about another person. Lashon hara differs from defamation in that its focus is on the use of true speech for a wrongful purpose, rather than falsehood and harm arising. By contrast, hotzaat shem ra ("spreading a bad name"), also called hotzaat diba, consists of untrue remarks, and is best translated as "slander" or "defamation". Hotzaat shem ra is worse, and consequentially a graver sin, than lashon hara.
Speech is considered to be lashon hara if it says something negative about a person or party, is not previously known to the public, is not seriously intended to correct or improve a negative situation, and is true. Statements that fit this description are considered to be lashon hara, regardless of the method of communication that is used, whether it is through face-to-face conversation, a letter, telephone, or email.
The noun lashon, "tongue", followed by the definite article ha and the adjective ra, "evil". The Hebrew noun lashon means "tongue", and as in many languages, "speech" or "language". The phrase is generally translated as "evil speech". The term corresponds to the idea of an evil tongue in other cultures, such as the Latin mala lingua, the French mauvaise langue, and the Spanish mala lengua.
The term lashon hara does not explicitly occur in the Tanakh, but "keep thy tongue from evil" (נְצֹר לְשֹׁונְךָ מֵרָע) occurs in Psalm 34:14. The Torah contains a general injunction against rekhilut (gossip): "Thou shalt not go up and down as a talebearer among thy people; neither shalt thou stand idly by the blood of thy neighbour: I am the LORD" (Leviticus 19:16). In addition, the words "ye shall not wrong one another" (Leviticus 25:17) according to tradition refer to wronging a person with one's speech.
The Talmud (Arakhin 15b) lists lashon hara as one of the causes of the Biblical malady of tzaraath. In Sotah 42a, the Talmud states that habitual speakers of lashon hara are not tolerated in God's presence. Similar strong denouncements can be found in various places in Jewish literature.
In Numbers chapter 12, Miriam gossips with her brother Aaron. She questions why Moses is so much more qualified to lead the Jewish people than anyone else. God hears and strikes her down with tzaraath. Miriam had to stay outside of the camp for a week due to the tzaraath. During this time, all of Israel waited for her.
Chafetz Chaim 
Rabbi Yisrael Meir Kagan wrote two major halakhic works on the evil tongue: Chafetz Chaim ("Desirer of Life") and Shmirat HaLashon ("Guarding the tongue"), both 1873. The Chafetz Chaim lists 31 speech-related commandments mentioned in the Torah. An English translation, Guard Your Tongue, (2002) anthologizes the teachings of these two books.
There are times when a person is supposed to speak out, even though the information is disparaging. Specifically, if a person’s intent in sharing the negative information is for a to’elet, a positive, constructive, and beneficial purpose, the prohibition against lashon hara does not apply. If the lashon hara serves as a warning against the possibility of future harm, such communication is under certain conditions, compulsory. Hotzaat shem ra, spouting lies and spreading disinformation, is always prohibited.
See also 
- Judaism 101: Speech and Lashon Ha-Ra
- A Commentary on Catullus - Page 19 Robinson Ellis - 2010 re the Virgilian motto: " "baccare frontem cingite, ne vati noceat mala lingua futuro" .... would seem to show that the notion of witchcraft was originally that of the evil tongue (mala lingua) rather than the evil eye."
- John A. Lent -Third World mass media and their search for modernity Page 179 1977 "Lewis, writing about the features of West Indian society that make it more traditional than modern, delineated a number of interpersonal communications traits: Passion for intrigue; malicious gossip, the famous Trinidad mauvaise langue
- Caroline Sweetman Men and masculinity - Page 50 1997 "... to less acceptable but more aggressive methods of power enforcement such as spreading malicious rumours or mauvais langue".
- Cuban-American literature and art: negotiating identities - Page 24 Isabel Álvarez-Borland, Lynette M. F. Bosch - 2009 "The difference between the two organs is that whereas the diseased body is put in the care of medical specialists, responsibility for the ailing tongue, for la mala lengua, rests with the speaker alone. The only treatment available to ..."
- Cassell's Spanish dictionary: Spanish-English, English-Spanish Edgar Allison Peers - 1968
- Speaking for themselves: Neomexicano cultural identity Doris Meyer - 1996 "An article entitled "La lengua" [The tongue], appearing about the same time in El Nuevo Mundo [May 18, 1899], begins with the traditional equation between moral character and probity of speech. The image of a "mala lengua" [evil tongue]"
- Hebrew - English Bible / Mechon-Mamre Psalm 34:14
- Hebrew - English Bible / Mechon-Mamre Leviticus 19:16
- Hebrew - English Bible / Mechon-Mamre Leviticus 25:17
- Zelig Pliskin, Guard Your Tongue Bnay Yakov Publications (2002)
- Translation of Sefer Shmiras HaLashon
- Let Them Talk: The Mitzvah to Speak Lashon Hara by Rabbi Mark Dratch, JSafe
- A primer on how to raise our children to look at the positive and speak well about others
- 31 mitzvot of speech
- Hilchot Lashon Hara (L"H)
- Negative Speech (Lashon Hora) | Chabad.org
- Finding Your Zivug or Mate Loshon Hora and Information-Seeking in Shidduchim