Gathering (sewing) –
The process of reducing fullness at an edge until the desired length of the edge is reached.
Use multiple rows of loose stitching and pull the thread or make a zig zag stitch over
heavy thread and pull along the heavy thread.
Sew down and press to flatten to prepare for adding into a seam. Reduce bulk as needed.
This technique is used to create ruffles, gathered skirts, and more.