What are all of these terms?

When people talk about sets in PvP they usually say something like 40/40 or switching between two sets to hide your energy or a 15^50 dagger

what does this mean? The most i've seen a inscription or head be able to do is a 20% chance to reduce cast or rech so where do people get 40 from? What is the point of having these different energy sets? And i cant even guess what a15^50 dagger is

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Also This one

40/40 means 20% half skill recharge and 20% faster casting time chance on both a wand and an offhand. 15^50 means 15% damage while health is over 50%.

alright thanks

also what does a spear/shield defensive set mean? Is it a shield with + hp and the 20% to reduce dmg by 5 and the spear with HP?

The 20% chance to reduce physical damage by 5 is one of the worst inscriptions. Defensive means fortitude and +10 armor vs one specific kind of damage on the shield.

What notskorn said, but if you want a damage reducing shield, get one that's -2 while in a stance or -2 while enchanted or, if you're rich/lucky - both.