In sewing instructions, they will tell you to baste and/or later to easestitch, here is an explanation:
Basting, either by hand or machine, temporarily holds something in place
before final stitching. Easestitching, along the seamline or just
inside the seam allowance, is done by machine. It gathers the slight
fullness at the edge of one piece of fabric before it is sewn to another
piece, which is shorter.
Typically it's a really long stitch that you use to gather the fabric up a little so that you can match up a long edge to a short edge. It's similar to basting, except you have to gather up the longer piece of fabric a bit.
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