To piggyback, an example of what you would see in the meld window could be something like:
Vitality: 20/20 Strength: 20/20 Critical Hit: 0/20 Determination: 15/20 Direct Hit: 10/20
These aren't actual stats, but just an example of what you may see. Vitality and Strength are 20/20, so they are capped and you cannot meld any more of them. However, Critical Hit is 0/20, meaning that you can meld up to 20 points of critical hit materia into the gear. Likewise with 5 points of Determination and 10 points of Direct Hit.
White gear can be pentamelded, meaning you can put up to 5 materia in it. Note that only the visible slots you see on the gear are guaranteed a 100% success rate. There are other, advanced melding slots where the percentage for success is lower (i.e., not 100%). All of the gear you can craft may be pentamelded, but some gear only allow 1~2 melds, and some none at all. The game will tell you if you cannot meld a piece of gear.
