Electrical current will pass easily through?

Copper, metal, aluminum.

I think the answer you are probably looking for is a conductor. Practical conductors are usually metal, although non-metals, such as carbon, are also commonly used. Liquid conductors are called 'electrolytes'. The best metallic conductor is silver, followed very closely by copper. In practise, copper is likely the most common metal conductor but, as copper is relatively expensive, aluminium is widely used for transmission and distribution lines.