What are the dark clouds in space?

The dark clouds in space are called absorption nebulas or dark nebulas. An absorption nebula is a cloud of gas and dust which blocks light from the regions of space behind it. As light from space reaches an absorption nebula it is absorbed by it and does not pass through. Absorption nebulas do not create their own light. It is hard to find an absorption nebula unless it is silhouetted against much brighter region of space.