It's a catch-all for the tech capabilities of a civilization. Expressed in terms of energy harvesting. Eg. capturing all energy output of a star, includes the

It's a catch-all for the tech capabilities of a civilization. Expressed in terms of energy harvesting. Eg. capturing all energy output of a star, includes the ability to move (vehicles, robots etc) through space, build star-sized infrastructure, and so on. Personally I prefer the magnitude of energy production/consumption. MWatt → GW → TW etc. Or how advanced (or energy-dense) its source is: Burning stuff → electric power → nuclear fission → nuclear fusion → antimatter