The middle part, with the center bolt, is the thru the firewall connection to the back side of the inside fuse panel. Right above that is a couple of circuit breakers and wiring that have been added by someone to power something.
On later models it's covered from the factory with a piece of plastic wrap and some black sealer. It's right above the battery in this shot. That spot can get wet as it's right below the hood hinge and water can drip onto the wiring and the top of the battery.
Can cause the wiring connections to corrode.