Mastery

Experience, Levelling and Mastery:

Level and EXP: Depending on the Level in the Zone you're in and your Mastery Levels you will gain less EXP for the remaining Mastery Branches.

Example: If you have Mastery 30 in Combat, Drones and Mining you won't gain much EXP for Salvage Tasks in lower Level Areas. To Level up salvage in this case head to a higher level Sub-System than you are currently in.

Mastery: Mastery as the name implies is getting gud in a given Skill Branch. Mastery will give you a Bonus, check the Level and the Bonus when hovering over Mastery in "Skills" under the "Captain" Menu.