Bolometric correction is a difference in magnitude applied to stars to determine their bolometric magnitude from their visible magnitude. It varies by type of star, e.g., spectral class, and is largest for stars much hotter or cooler than the Sun because the EMR from stars of the Sun's temperature is centered around visible light.
Some bolometric correction examples:
|O3 star||-4.3 for a main sequence star||-4.2 for a giant|
|G0 star||-0.10 for a main sequence star||-0.13 for a giant|
|M0 star||-1.21 for a main sequence star||-1.28 for a giant|