Paint correction is the process of restoring and rejuvenating the paintwork of a vehicle, mostly through the elimination of surface imperfections, that dull, oxidize, or haze the surface by reflecting light off in various directions, therefore detracting from a true and proper, clean, sharp, reflection. These imperfections include things like swirl marks & fine scratches, bird dropping etching & acid rain etching, hologramming & buffer trails, and random isolated deep scratches.
A fully corrected vehicle when viewed in direct sunlight will show only true reflections and no swirl marks, scratches or blemishes will be visible to the naked eye.
Lastly, it is important to distinguish between paintwork that has been truly corrected and paintwork that has been treated with products that are designed to mask and fill surface imperfections such as an all in one polish for example. This should not be referred to as paint correction even if no scratches or blemishes are apparent, because they have not been genuinely removed and are still present under the products fillers, which in time, will wash away and reveal them once more.