A Must Match skein has two perfectly matched half skeins which start and stop in the same place of the striping sequence for identical knits with no waste. I specially dye the matching halves at the same time so they are usually identical almost down to the stitch! This type of skein was formerly known as OCD.
In the picture shown below, you will notice that where the two ends are tied together that one end is black and the other is orange with just a tiny bit of yellow at the very end. This is a very good example of how close the two skeins usually are.
Almost Every skein for sale is a Must Match skein. Occasionally, there will be non-Must Match skeins offered for sale. Examples of non-Must Match skeins include Whole or Companion skeins and these will be clearly labeled as such.