dont talk to me about dye lots I do not see it 😑😭
Based on your tags this seems like a genuine question. Basically yarn is dyed in batches and each batch is given a number. Even big yarn brands like Lyon and stuff will have slight color differences between batches. Because of this it's a best practice to purchase yarns all from the same batch.
The dye lot number is the number of the batch and it will be printed somewhere on the label for the yarn. Ideally, you want all the dye lots for skeins in a given project to match. Depending on the type of yarn coloration and difference between the dye lots, it may not matter very much, but it could also matter a lot. It all depends and is just something to keep in mind.
In my experience, the yarn currently stocked in a store for each color, is usually the same dye lot. The problem is usually something you run into if you need to purchase additional skeins months down the road and the original dye lot you purchased is all sold out.
TLDR: it's a numbering system that matches yarn skeins to dye bath batches by number. Depending on the type of yarn the color may vary a little or a lot in between batches.
