A boom is an adjustable arm that is mounted at an angle from a vertical pipe or stand. The boom is usually counter-balanced and is used to hold lighting or sound equipment. It looks a lot like a tripod with a center post in it. A boom stand can hold assorted lighting equipment such as a boom and softbox, but you can also use one to mount your continuous lights and strobes.
Make sure your stand is strong, durable and flexible. Most of them are made of steel for extra strength. It should also be adjustable, so you can use it on non flat surfaces. A good stand should also have wheels on it so you can move it around in the studio. Boom stands come in various materials, brands and sizes. They range in price from about $40 to over $1,000 for a kit.