When you velcro something, you close or secure it using a fastener with tiny plastic hooks that adhere to tiny loops when you press them together. You should velcro your little sister's boots before she runs outside to play in the snow.
As a noun, Velcro is capitalized, since it's a trademarked brand. The man who made it possible for us to velcro any number of things, from dog jackets to electric cord holders to umbrella covers, was Georges de Mestral, a Swiss engineer. He noticed the way burrs stuck to his dog's fur after a walk in the woods, studied the shape of the burrs under his microscope, and spent 14 years developing Velcro.