Definition
The JCPOA was the 2015 multilateral agreement between Iran and the P5+1 (US, UK, France, Russia, China, Germany) under which Iran limited its enrichment activity and submitted to enhanced IAEA monitoring in exchange for relief from nuclear-related sanctions. The agreement was effectively unwound after the 2018 US withdrawal.
Why this matters when reading conflict news
Almost every current Iran-nuclear story references the JCPOA as the baseline against which current enrichment levels and oversight arrangements are measured.