Bias tape is fabric binding that’s used on many sewing and quilting projects. It’s essentially a strip of fabric cut on the bias that’s folded 3 times to make a little case around the edge of another piece of fabric to “finish” it. Cutting fabric on the bias means cutting at a 45 degree angle from the fibers. This allows the strip of fabric to have some stretch to it.
You can sew many of these strips together for a long tape to use on larger projects.
You can buy it pre-made in solid colors or you can make your own out of any fabric you want.