Definition of "transboundary"

Emphasizing that it has applied equitable apportionment to not only rivers and streams but also to interstate river basins, to groundwater pumping that affects surface water flows, and to anadromous fish like Chinook salmon and steelhead trout, the court stated that equitable apportionment applies only when transboundary resources are at issue.

2021 November 23, Robin Craig, “In dispute over groundwater, court tells Mississippi it’s equitable apportionment or nothing”, in SCOTUSblog