In The Mishnah
The expression tikkun olam is used in the Mishnah in the phrase mip'nei tikkun ha-olam ("for the sake of tikkun of the world") to indicate that a practice should be followed not because it is required by Biblical law, but because it helps avoid social disharmony. One example is in Gittin 4:2.
At first a person used to convene a Court in another place and cancel it. Rabban Gamliel the Elder enacted in the public interest (mip'nei tikkun ha-olam) that they should not do so. At first a person used to change his name and her name, the name of his city and the name of her city, and Rabban Gamliel the Elder enacted in the public interest (mip'nei tikkun ha-olam) that he should write, "The man so-and-so and every name that he has," "The woman so-and-so and every name that she has."
The rabbis made this rule because they were concerned that a woman might receive a get (divorce document) and think she was divorced when in fact she was not (because the man had voided the divorce in a court). She might then remarry in good faith not knowing that she was not yet a free woman. In Jewish tradition there are severe consequences if a married woman engages in sexual relations outside of her marriage. She may not marry the man with whom she had sex and her children are ineligible to marry most other Jews because they acquire the technical status of mamzerim.
As an explanation of rabbinic laws, the phrase mip'nei tikkun ha-olam is also invoked for laws about the collection of the ketubah money for a widow (Gittin 4:3), the limit on payments to redeem captives (Gitten 4:6), purchasing religious articles from non-Jews (Gittin 4:6), divorce threatened by vows (Gittin 4:7), and the bringing of first fruits for land purchased from non-Jews (Gitten 4:9). Several additional uses are found in Gittin 5:3.
During the Talmudic period, the principle of mip'nei tikkun ha-olam is applied to a very limited number of additional cases. (For example, see Pesahim 88b.) In both the Mishnah (Gittin 4:6) and the Talmud, applications of the principle are contested at times.
Read more about this topic: Tikkun Olam