velcro is a brandname and trademark owned by the velcro companies for "hook-and-loop fasteners". hook-and-loop fasteners have a "hook" side, which is a piece of fabric covered with tiny hooks, and a "loop" side, which is covered with even smaller and "hairier" loops. when the two sides are pressed together, the hooks catch in the loops and hold the pieces together. when they are separated, they make a special "ripping" sound.