@julie Hiya, im a telco installer. That looks like your bonding wire for the protectors on the twisted pair or coaxial coming into your home. It should be bonded to your houses ground at some point. Different jurisdictions have different rules. Contact your Telco if you have phone or adsl. If you have cable contact them let them know you are not properly bonded at your protector. That demarc looks like phone company to me.