Growth Factor
Growth Factor in the Stellaris encyclopedia: Growth Factor is a measure of the quantity of nutrients absorbed by your Behemoth, and affects how fast the situation will progress.
Growth Factor in the game's words
The encyclopedia entry as the game shows it in its tooltips; underlined words open their own entry or page here.
Growth Factor is a measure of the quantity of nutrients absorbed by your Behemoth, and affects how fast the situation will progress.
Every month, it decreases by 0.75%
Increase your Growth Factor by:
- Killing other Behemoths, Leviathans or Biological Ships
- Eating Habitable Planets.
- Eating 
Pops.
The Minimum Value is equal to 0.5% per 100 Transferred Pops.
Source: common/game_concepts (concept_growth_factor) and localisation/english, Stellaris Cygnus v4.5.2 (9776).