It is whatever your game plan requires; properly geared can mean that your character functions well as a hybrid; it can mean that your tank can soak up a certain amount of damage for an encounter (say 400+ magic armor or physical armor before buffs); it can mean that every party member is capable of one shotting most given encounters.
So, the question is, what is your game plan? Then you can answer what properly geared means to you. For me, it was simply to push damage, memory, bartering, and leadership as high as possible so I could be as flexible as possible in terms of buying power and deal with any given encounter.
Okay, I've seen you post a lot on these forums, and you honestly seem really knowledgeable. So how do you get these sorts of numbers? I thought I was doing good when I found a +2 memory item, and I found it on the last boss, so at that point it didn't even matter. I still can't find any good INT items past a really good staff that I stole, and my warrior has yet to see a strength item. Not to mention, the highest magic armor item I have is a necklace that gives +42 magic armor or something like that, on my 2 player game, and I've been everywhere I could find. I have thievery 4, and I've been stealing the best stuff I can find, but what's the secret?