Black Rat Snake

I think it's an eel

This is either a Black Rat Snake, or a Black Racer. Either way, it's definitely NOT DANGEROUS. They will only bite in self-defense (although I've picked up adults of both species with no problem. I don't recommend you try it though.) They will help keep rodents out of your home, so not to worry if he's seen slithering around your yard. Just leave it alone and it will be very happy to leave you alone too. :)