What does 7018 stand for on welding rod?

70 stands for 70,000 lbs tensile strength in the "as welded condition" - untreated, 1 means it can be used in any position (flat, vertical, horizontal, overhead) 18 tells you it can be used with AC or DC Reverse Polarity. It also tells you what the base compound is in the coating. It is not recommended to be used vertical downhand.