Nebulas come from  Greek meaning "mist". Nebula can be spelled two ways.  There is "nebula' and "nebulae".   Nebulas are simply clouds of gas left over from exploded stars.  One famous nebula is the Crab Nebula.  It is the remnants of a super nova that happened in 1054.  In the center of the Crab Nebula is a pulsar.  Nebulas are quite amazing to see.  I hope you take advantage whenever you see one.