Reading up on "constant voltage charging" and it refers to the voltage at the charger. "Constant current charging" is used for the Bulk stage instead, so the amps don't taper right away and you get faster charging.
"Multi-stage" chargers do both. Constant Current for Bulk and then trip to Constant Voltage for Absorption to protect from overcharging. But battery voltage keeps rising during both stages.
"Constant voltage charging" is slower. (Because amps taper from the start) and is only suitable when the battery is shallow cycled. It is not suitable for deep cycle recharging.
And--Anybody who thinks you can have constant voltage at the battery terminals while the battery voltage is constantly rising must be bonkers IMO.
