The descriptions used here seem somewhat arbitrarily different from the tooltips in the UI, and leave out some details. I prefer the tooltips.

None: Do not use this surface as a light for sampling
Auto: Automatically determine if the surface should be treated as a light for sampling, based on estimated emission intensity
Front: Treat only front side of the surface as a light, usually for closed meshes whose interior is not visible
Back: Treat only back side of the surface as a light for sampling
Front and Back: Treat surface as a light for sampling, emitting from both the front and back side

I think "directly sampling" is not so clear, "use as a light for sampling" I think more clearly hints at how this will behave. The point about closed meshes for Front I think is also important to keep.