what's mean "ref" in the trades?

Refined Metal, its something you can get from Team Fortress 2. It has no value on its own, but can be refined into other stuff, so eh.

The best metal you can craft in TF2. This one

Refined metal from Team Fortress 2. Worth around $0.25, and 7~8 refs worth 1 key.

It's what I have in my inventory

One of the items in tf2 ranked as currency. If you get 9 scrap metal (18 unique-graded weapons) you can get a refined. You have to make 3 reclaimed metal (1 rec=3 scrap, 1 ref=3 rec)

refer ;)-~

spiek english you well...

jk

It's a trading currency. Chances are you won't need it unless you're heavily into trading.