I would like to replace this light switch but I can't figure out what kind of light switch this is. Is it a single pole light switch or three way switch? The only hot wire is the black wire - this box only has a single romex cable in it with a black, white and ground wire. What is the white wire doing, is that connected to the ground screw? The actual ground wire was up against the box screwed tight with the top screw of the actual outlet itself.
The switch is a double throw for a 3-way switch circuit. However, it is used as a single pole switch.
The circuit is a "switch loop" that uses the white wire to carry power from the switch to the device it services. The white wire should be marked with some black tape, or colored with a black marker.
If you want to replace the old switch, just use a single pole switch. Black on one brass screw, white on the other brass screw, ground to the ground screw.