Max weapon or armor

How can I tell if a weapon or amor has been maxed?

It really depends on what type of weapon, and armor depends on which profession you chose. Visit the Armor and Weapon pages of The Official Guild Wars Wiki for everything you're asking to know.

Each weapon type has a fixed maximum damage range. They are listed on the wiki. As for armors, max armor level for a caster is 60, for rangers and dervishes it's 70 and for warriors and paragons it's 80. That's without any insigna on the armors.

I meant to ask how many upgrade I can do on the weapon or armor before it max out (socket full.... if there is such thing as socket)?

And when people talked about max out weapon/armor, do they mean max the dmg for weapon and the def for armor? Or do they talk about filling in all the open socket on items?

Traditional:

-Staves: Head Piece, Wrapping, Inscription - (Prefix, Suffix, Inscription)
-Melee: Prefix, Suffix, Inscription
-Wands: Inscription + Wand Wrapping (nightfall only thus far)
-Shields: Inscription + Handle (nightfall)
-Focus Item: Focus Core + Inscription (nightfall)
-Armor: Insignia + Rune

So armor, shields and focus items have two upgrades, while melee items and staves have three.

A "max" weapon refers to either:
-An item in which the base damage is in its maximum range (common.) In other words, daggers are 7-17, swords are 11-22, etc.
-A item that is fully modded and inscribed (secondary.) A sword that is +15% BASE damage when health is above fifty percent (15^50), Vampiric (3/-1) and has armor +5. This is, of course, an example, the sword that is described is not the "max" for all swords, but simply one that is fully inscribed and modded.

There exists no "max" item in the sense that it is more powerful than all the rest. Each mod/inscription contributes to a build and are weighed only on their effectiveness with /that/ particular build. For instance, the ongoing debate of Vampiric vs. Sundering (though Sundering is good for Heroes, IF the choice is between only Vampiric and Sundering.)