I may have the terminology wrong, but I believe it's "equalizing."
Basically, controlled overcharging of the battery reverses the sulfur reaction and restores the battery, somewhat. Modern electronically controlled chargers probably have programmed settings, but the old school way is a charger big enough to overcharge the battery while you watch the temperature to prevent plate buckling.
I have a lot of experience in ruining batteries. Either overcharging them or discharging them to the point where they sulfate. If you want to learn about battery failure modes and their potential remedies, it comes with a high tuition.