Ask ten different experts the difference between piping and cording and you might get ten different answers. however, you can be sure it does NOT have anything to do with bagpipes or comfortable pants.
Piping and cording are the outlines of home decor. They provide a coordinating or contrasting edge along the seams of slip covers, cushions, pillows and more. You simply sew the piping or cording into your seam and it gives a professionally finished look. Some home dec professionals prefer the term "welting" when referring to this feature on pillows, cushions and the like, because they feel piping belongs to the world of garment sewing. Take your pick.
The confusion may come from the fact that all piping is made with cord. Piping cord is a thin, round cotton "rope" made especially for sewing. It comes in a variety of thicknesses, depending on how full you want your finished piping to be.
To make piping, you take a bias strip and fold it over the piping cord. To attach it to your article you sew the open end into the seam.
Because of the cord inside, many home decor experts will refer to this as cording.
Whatever you like to call piping, you can get it several different ways. You can purchase it ready-made, though your color choice will be limited. You can buy bias tape and piping cord to make it yourself. Or, if you want your piping to exactly match the the rest of your project (often the choice for cushion covers and upholstery), you can buy just the cord and cut your own bias strip out of your fabric.
If you go into a fabric store and ask for cording, they will most likely show you decorative cord that is attached to a narrow strip of fabric for insertion in your seam. It's often braided and made from shimmery or metallic fibers to make an elegant accent.
This kind of cording is a favorite on pillows and cushions.
If you are going to wash the item you're making, you should always preshrink (prewash) your cording and piping. However, decorative cording often goes on items that you won't be throwing in the washing machine.
If you make your own piping just be sure to cut out your bias strips after you've washed your fabric. If you don't, items like slipcovers, pillow covers and cushion covers will pucker along the seams.