Well the dark is 'dark' because no light is let in. Places like an enclosed area with walls and ceilings also no lights are dark. It is dark because no light can get through the enclosure you are in.
It is definitely "People Under the Stairs". (different person) i myself actually think it is tales of the crypt. (another person) there was a book about skeletons with this begining. i think it was...
Dark energy is the force that expands the universe. Dark matter is the force that keeps everything from crashing into one an other. Dark matter is what keeps galaxies together for example if you pour...
Both dark matter and dark energy are "dark" because they give off no visible light. Think of it... The universe is filled with literally trillions of stars, all giving off tremendous loads of light....