The phrase "armor upgrades" refers to improvements or additions made to protective gear or clothing, such as making it stronger, more resistant, or adding extra features for better defense. Full definition
On top of all of that, the game features a full level / experience system, in addition to the souls / weapon / armor upgrade system that has existed throughout the series. (namakoteam.com)
Loot collected from fallen foes can be used to create new equipment and armor upgrades as players seamlessly move across map areas that comprise the living ecosystems. (co-optimus.com)
This Final Fantasy Explorers guide provides detail on how to Armor and Armor upgrades work, stats and many other things. (gamepur.com)