From the Summary: "When there is concern with deficit or debt levels, Congress will sometimes implement budget enforcement mechanisms to mandate specific budgetary policies or fiscal outcomes. The Budget Control Act of 2011 (BCA; P.L. 112-25), which was signed into law on August 2, 2011, includes several such mechanisms. The BCA as amended has three main components that currently affect the annual budget. One component imposes annual statutory discretionary spending limits for defense and nondefense spending. A second component requires annual reductions to the initial discretionary spending limits triggered by the absence of a deficit reduction agreement from a committee formed by the BCA. Third are annual automatic mandatory spending reductions triggered by the same absence of a deficit reduction agreement. [...] This report addresses several frequently asked questions related to the BCA and the annual budget."
CRS Report for Congress, R44874
Congressional Research Service: https://crsreports.congress.gov/