Metal spike with heavy metal cord found in front lawn
It's a grounding rod, probably 8 or 10 feet long, such as is required for any residential installation. They're usually proximal to the breaker panel or fuse box in the home or outbuilding. You may have encountered an obsolete one that's been disconnected. You'll need to trace the bare copper wire to be sure. 

You can drive it down below the surface if you like. Try not to damage the wire, which can also be buried a bit deeper without causing problems.