A typical band clamp consists of a strap and some type of screw or ratcheting mechanism for securing the band and applying pressure.
Sometimes referred to as a web clamp, this tool is ideally suited for objects with surfaces that are not parallel to each other; where there are multiple planes involved; or where clamping pressure is required from several directions at once.
The clamp used in this video has corner brackets that hold miters at 90 degrees which makes it well-suited for assembling a frame or case. While a band clamp will apply pressure simultaneously to all four joints of a rectangle, it will not necessarily keep the assembly square. Always, check the angles with a carpenter’s square or measure across the diagonals and insure they are equal.
The bands or webs come in different widths and lengths (up to 25 feet, or more).
Here are some links to a few of the more common styles and types.