basicly one side is a whole bunch on tiny hooks, the other side is a bunh of tiny loops, when pressed toghter the hoods catch in the looks. Hence hook and loop. and like audiboy said, velcro is just a brand
And since Velcro® is a trademarked name, companies can't use it unless they are using material from that particular company. Like saying "Crescent wrench" for an adjustable wrench. Technically, it's just an adjustable wrench unless it's made by the Crescent company, and the Crescent company makes a few tools, so even that can be a misnomer.