Correction filters are the output of room correction software: based on measurements from a calibration microphone, the software calculates the inverse of the room's frequency and phase problems. The filter boosts frequencies where the room creates a null and cuts where the room creates a peak (though boosting nulls is limited because nulls are cancellations — adding more energy just creates more cancellation).
Correction filters are typically applied as a system-wide EQ (in your DAW monitor chain, a hardware DSP box, or software like Sonarworks). They work best for frequencies above the room's transition frequency (~200–300 Hz). Below that, acoustic treatment is more effective than DSP correction.