Question. What is a interstellar cloud?


Answer. The vast speaces between stars are not empty but contain particles of matter and larger grains dust. In some places this interstellar material has been swept up into giant dense clouds.  Some of these clouds will streach across tens of lightyears and contain thousands of times the mass of our sun.  Stars form inside these clouds when gravity causes a small chunk of the cloud to collapse on itself.
 

Below is an image of the an interstellar cloud from the Hubble Space Telescope