Referred to as shirring. Nevertheless, the seem it results in is similar to smocking, which is an embroidery technique that’s existed a long while. But maybe don’t google “precisely what is smocking” cuz apparently Furthermore, it refers to a thing that has very little to carry out with sewing… Anyway, https://coveredspandexyarn78887.blog2freedom.com/31689113/helping-the-others-realize-the-advantages-of-rubber-covered-yarn