A nebula from Latin: "cloud"is an interstellar cloud of dust, hydrogen, helium and other ionized gases. Originally, nebula was a name for any diffuse astronomical object, including galaxies beyond the Milky Way.
This image from Nasa's Spitzer Space Telescope shows a stellar nursery containing thousand of young stars & developing protostars near the sword of the constellation Orion. I heart the Spitzer space telescope.
"The Cartwheel Galaxy" - Located 500 million light-years away in the constellation Sculptor, the galaxy looks like a wagon wheel, an unusual configuration created by a nearly head-on collision with a smaller galaxy about 200 million years ago.