Tikkun olam (repairing the world)
Who
Rabbinic and kabbalistic Judaism
When
2nd century onward
Where
The Land of Israel, then Safed
The phrase appears in the Mishnah as a reason to amend law for the sake of an orderly society, and is recast by the sixteenth-century kabbalists of Safed as a cosmic task: the world is broken, and human acts help mend it. In modern usage it is the common Jewish shorthand for the duty to leave the world better than you found it.
Sources
Part of “The Gifts of the Jews” — verified Jewish contributions to the world, with sources.