Vibranium is a fictional element found in Marvel comics and has been utilized by various characters to create varied weapons and gadgets - one of the most famous of which is Captain America's Shield.
Vibranium has the ability to absorb all vibrations in the vicinity as well as kinetic energy directed at it. The energy absorbed is stored within the bonds between the molecules that make up the substance. As a result, the more energy vibranium absorbs the tougher it becomes.