Charge
The amount of powder, measured in grains, loaded into a cartridge. Each combination of cartridge + bullet + powder has a usable charge range.
For a 140 grain 6.5 Creedmoor bullet over H4350, the usable charge range is roughly 39.5 to 42.0 grains. The starting charge is typically 92% of the published maximum; the load development process works upward in 0.2-0.5 grain increments, watching for accuracy nodes and pressure signs.
Throw charges with a quality scale, not a volumetric thrower, if you care about ES. A 0.1-grain error at the powder level changes velocity by 5-10 fps.