Ply and gauge are terms used to describe the way a jumper is knitted: it does not refer to the quality or value of the sweater. The weight of your jumper directly determines its value: the heavier the knit, the more expensive it becomes as more material has been used to make it.
What is Ply?
The twisting process helps to form yarn much like braiding your hair.
2-ply yarn consists of two strands twisted in opposite directions and then twisted together to create resistance.
By using 2-ply yarn, your jumper will hang straight and luxuriously.
A sweater made with a single ply only has motion only in one direction and this can cause your jumper to warp and hang rather badly.
Also, the thicker the ply, the heavier and warmer your jumper becomes.
What is Gauge?
Guage is the number of needles used per inch.
The higher the gauge, the more tightly knit the sweater is.