What do they mean by "single drawn"?

Single drawn and double drawn are the terms commonly used by manufacturers of hair extensions and not widely used by salons. If you’re looking to buy a set of extensions online or from your salon it’s very important to know the difference.  All human hair grows in cycles. While some are growing, some are dormant. This is the reason there are so many lengths in a single drawn ponytail.  Single Drawn hair means only the very shortest hairs have been combed out, usually first 2 or 3 inches. So if you had 18″ length hair, some strands will be as short as 14, 16"″. Double Drawn hair is the absolute best quality hair. The term refers to a process that draws out all the shorter lengths from a bundle, and then draws again to realign the top of the bundle. The hairs are arranged in equal lengths creating a very smooth and polished look. This increases the cost of hair as this procedure is done by hand.