Items labeled Precious.

Can someone explain to me why some Blue text items is labelled "Precious"?

It is a random bonus, like highly salvageable. If an item is "precious" it will be purchased by an NPC merchant for slightly more than other blue items with similar stats. If an item is "highly salvageable" then it will produce larger quantities or more valauble varieties of materials when salvaged. Neither random bonus has any effect on gameplay, so statistical bonuses are superior (like 15>50) and thus gold items have those better bonuses that actually make a difference with how effective the weapon is.