What is Tikun Olam?
(א) לֹֽא־תִרְאֶה֩ אֶת־שׁ֨וֹר אָחִ֜יךָ א֤וֹ אֶת־שֵׂיוֹ֙ נִדָּחִ֔ים וְהִתְעַלַּמְתָּ֖ מֵהֶ֑ם הָשֵׁ֥ב תְּשִׁיבֵ֖ם לְאָחִֽיךָ׃ (ב) וְאִם־לֹ֨א קָר֥וֹב אָחִ֛יךָ אֵלֶ֖יךָ וְלֹ֣א יְדַעְתּ֑וֹ וַאֲסַפְתּוֹ֙ אֶל־תּ֣וֹךְ בֵּיתֶ֔ךָ וְהָיָ֣ה עִמְּךָ֗ עַ֣ד דְּרֹ֤שׁ אָחִ֙יךָ֙ אֹת֔וֹ וַהֲשֵׁבֹת֖וֹ לֽוֹ׃ (ג) וְכֵ֧ן תַּעֲשֶׂ֣ה לַחֲמֹר֗וֹ וְכֵ֣ן תַּעֲשֶׂה֮ לְשִׂמְלָתוֹ֒ וְכֵ֣ן תַּעֲשֶׂ֜ה לְכָל־אֲבֵדַ֥ת אָחִ֛יךָ אֲשֶׁר־תֹּאבַ֥ד מִמֶּ֖נּוּ וּמְצָאתָ֑הּ לֹ֥א תוּכַ֖ל לְהִתְעַלֵּֽם׃ (ס) (ד) לֹא־תִרְאֶה֩ אֶת־חֲמ֨וֹר אָחִ֜יךָ א֤וֹ שׁוֹרוֹ֙ נֹפְלִ֣ים בַּדֶּ֔רֶךְ וְהִתְעַלַּמְתָּ֖ מֵהֶ֑ם הָקֵ֥ם תָּקִ֖ים עִמּֽוֹ׃ (ס)

(1) If you see your fellow’s ox or sheep gone astray, do not ignore it; you must take it back to your fellow. (2) If your fellow does not live near you or you do not know who she is, you shall bring it home and it shall remain with you until your fellow claims it; then you shall give it back to her. (3) You shall do the same with her donkey; you shall do the same with her garment; and so too shall you do with anything that your fellow loses and you find: you must not remain indifferent. (4) If you see your fellow’s donkey or ox fallen on the road, do not ignore it; you must help them lift it.

ואיזוהי מצות עשה שלא הזמן גרמא מזוזה מעקה אבידה ושילוח הקן

And what is a positive mitzvah that is not time bound? Examples include putting up a mezuza, the construction of a parapet on a roof, returning a lost item, and the release of the mother bird from the nest.

אֵין מוֹצִיאִין לַאֲכִילַת פֵּרוֹת וּלְשֶׁבַח קַרְקָעוֹת וְלִמְזוֹן הָאִשָּׁה וְהַבָּנוֹת מִנְּכָסִים מְשֻׁעְבָּדִים, מִפְּנֵי תִקּוּן הָעוֹלָם. וְהַמּוֹצֵא מְצִיאָה, לֹא יִשָּׁבַע, מִפְּנֵי תִקּוּן הָעוֹלָם:

The court does not appropriate liened property that has been sold to a third party for the consumption of produce or for the enhanced value of land. [If one appropriated (stole) a field and sold it, and the buyer worked the land, enhanced it, and grew produce on it, and then the initial owner from whom the field had been stolen took back the land and the produce from the buyer, compensating them only for expenses, then the buyer may go back to the seller, i.e., the robber, and collect her losses.] And similarly, payment for the sustenance of a man’s wife and daughters cannot be collected from his liened property. [One of the stipulations included in a marriage contract is that after the husband dies, his widow and daughters are entitled to sustenance from his estate. This sustenance cannot be collected from husband’s liened property that has been sold to another person, but only from his unsold property inherited by his heirs.] All of these enactments were made for the betterment of the world. And it was further instituted that one who finds a lost item and returns it to its rightful owner is not required to take an oath that they did not keep any part of the lost item for themself. This ordinance was also instituted for the betterment of the world.

גְּמָ׳ מִפְּנֵי תִּיקּוּן הָעוֹלָם?! דְּאוֹרָיְיתָא הִיא, דִּכְתִיב: ״מֵיטַב שָׂדֵהוּ וּמֵיטַב כַּרְמוֹ יְשַׁלֵּם״!

GEMARA: [When the mishnah says: For the betterment of the world, it seems to be referring to all of the cases in the mishnah.] The Gemara therefore asks: [The first clause of the mishnah states that compensation for damage is collected from superior-quality land.] Is this ordinance also only for the betterment of the world? This is by Torah law, as it is written: “Of the best of his own field, and of the best of his own vineyard, shall he pay” (Exodus 22:4).

(ד) כִּ֤י יַבְעֶר־אִישׁ֙ שָׂדֶ֣ה אוֹ־כֶ֔רֶם וְשִׁלַּח֙ אֶת־בְּעִירֹ֔ה וּבִעֵ֖ר בִּשְׂדֵ֣ה אַחֵ֑ר מֵיטַ֥ב שָׂדֵ֛הוּ וּמֵיטַ֥ב כַּרְמ֖וֹ יְשַׁלֵּֽם׃ {ס}

(4) When any party who owns livestock lets it loose to graze in another’s land, and so allows a field or a vineyard to be grazed bare, restitution must be made for the impairment of that field or vineyard.

א כִּי צָרִיךְ כָּל אָדָם לוֹמַר: כָּל הָעוֹלָם לֹא נִבְרָא אֶלָּא בִּשְׁבִילִי (סנהדרין לז). נִמְצָא, כְּשֶׁהָעוֹלָם נִבְרָא בִּשְׁבִילִי, צָרִיךְ אֲנִי לִרְאוֹת וּלְעַיֵּן בְּכָל עֵת בְּתִקּוּן הָעוֹלָם, וּלְמַלְּאוֹת חֶסְרוֹן הָעוֹלָם, וּלְהִתְפַּלֵּל בַּעֲבוּרָם.

Now, each person must say: “The entire world was created only for my sake” (Sanhedrin 37a). Consequently, because the world was created for my sake, I must constantly look into and consider ways of making the world better; to provide what is missing in the world and pray on its behalf.

וְאֵיזוֹהִי מִצְוַת עֲשֵׂה שֶׁלֹּא הַזְּמַן גְּרָמָהּ – מְזוּזָה, מַעֲקֶה, אֲבֵידָה, וְשִׁילּוּחַ הַקֵּן.
And what is a positive mitzva that is not time bound? Examples include the affixing of a mezuza (Deuteronomy 11:20), the construction of a parapet on a roof (Deuteronomy 22:8), returning a lost item (Deuteronomy 22:1–3), and the release of the mother bird from the nest, i.e., the mitzva of sending away a mother bird when one finds it sitting on chicks or eggs (Deuteronomy 22:6–7).