I'm about to pull my hair out. What are these "Treasure-Seeker's" gear pieces I've picked up? I have scoured the internet and can't find out ANYTHING about them.

I honestly dont even know where I got them. Delve maybe? I have Googled every combination of words on earth to figure out WTF these things are and what they do but found nothing other than item pages on wowhead which tell you nothing. I just came back after skipping an expac so if this is supposed to be obvious I aint getting it.

"Your spells and abilities have a chance to excavate increasingly rarer treasures, granting you up to 249 Agility for 20 seconds. Resets after 3 excavations."

How does this excavate treasures?

What kind of treasures?

What exactly are the excavations it mentions at the end? Is that just a way of saying " resets after this effect has happened 3 times"?

Edited to reword a sentence.