WF stands for weighing forward fly lines. This refers to the taper of the line. On a weight forward fly line, the bulk of the taper is in the front of the line. This helps the line roll over between false casts and is great for distance casting. A DT line stands for double taper, this line has an even taper throughout the belly of the line. At each end, the line slightly tapers off to a thinner diameter. It's an easy line to cast but does not cast as far. That being said, the longer belly lines make it easier to roll cast. You can even flip the line around and double the lifespan of a line when the front half begins to wear out.