Sewing cording is about taking a little round cord and wrapping it with bias tape. Other common names for it are piping trim and welt trim.
I'm sure you've seen it somewhere, it looks like a little tube of fabric and It's always placed between two pieces of fabric.
It's mostly used for the edges of furniture, pillows, clothes and on bags. You can buy it, but making your own is better! Sometimes you can't find the right color or size.
If you make your own, you can choose the perfect size for your projects and make the piping match the main fabric.
Piping cord is a round and thick. It comes in many different widths and it's usually made of cotton. There's a special foot for sewing cording that has a channel to put the cord in. It's useful, but you can also use a regular zipper foot