Heter mechirah is a term which has been much in the news recently. It is a halachic device at the heart of arguments in Israel over the shmittah, sabbatical, year.
Heter means a leniency or loophole, from the word matir, to release or untie. Mechirah is a sale. The heter mechirah allows Jewish farmers in the Land of Israel to sell their land during the shmittah year. Doing so permits them to continue farming where otherwise they would have to let the land and themselves rest in the seventh year, as required by Leviticus chapter 25.
This seeming legal fiction was a compassionate solution to the shmittah problems of the Zionist agricultural pioneers who feared that strictly observing the sabbatical year would wipe out their fledgling farms and force them back to Europe.
Rabbi Yitzhak Elchanan Wasserman first issued the heter for the shmittah year of 1888-9, and Rabbi Abraham Isaac Kook repeated it in 1909-10. For Rav Kook, an ardent Zionist, the value of Jews returning to live in Israel justified employing the heter mechirah device.
Since the establishment of the State of Israel, the heter mechirah has been operated by the Chief Rabbinate. There were always those who preferred not to rely on it and ate imported or Arab-grown produce during the shmittah.
However, this shmittah year, the Chief Rabbinate has undermined the heter mechirah by allowing local rabbis the freedom not to give kashrut certification to produce grown under its dispensation. In response, a group of religious Zionist rabbis has, in defiance of the Chief Rabbinate, issued kashrut certificates to heter mechirah produce breaking the Chief Rabbinates monopoly over kashrut.