Obamacare just won a big victory from the Supreme Court. Again. On Thursday, the court ruled 6–3 to uphold the federal subsidies established by the Affordable Care Act. In his opinion, Chief Justice John Roberts explains that “the combination of no tax credits and an ineffective coverage requirement could well push a State’s individual insurance market into a death spiral. It is implausible that Congress meant the Act to operate in this manner.” Wait, you say! What exactly is the death spiral? What is this worst-case scenario that we just averted? Above, Slate explains.