Other kinds of welding. Some kinds of welding do not use an electric arc. They might use a flame, electricity without an arc, an energy beam, or physical force. The most common type of welding that does not use an arc is called gas welding.
TDW - Total Diamond Weight. A term usually used when there is more than one diamond in a particular piece of jewelry. The combined weight of all of the (diamond) stones.
TDS, or Total Dissolved Solids, is the measure of the sum of all the substances dissolved in your pool water. Everything you add to the water increases its TDS, including chlorine, shock, water balancers such as pH increaser or reducer, algaecide, clarifiers, etc.