What is MaxDOP controlling?

The Max Degree of Parallelism, or MAXDOP, is one of the most known settings in the SQL Database Engine. There are guidelines of how to configure it that have intricate dependencies on the type of hardware resources you’re running on, and there are several occasions where someone might need to veer of those guidelines for more specialized workloads.

There are plenty of blogs on these topics, and the official documentation does a good job of explaining these (in my opinion). If you want to know more about the guidelines and ways to override for specific queries, refer to the Recommendations