Historically, constellations were groupings of stars that were thought to outline the shape of something, usually with mythological significance. Their names tracing as far back as Mesopotamia, 5000 years ago.
Example below: the constellation Orion.
Mouse over to see the mythological interpretation.
Image NASA, www.hubblesite.org
In modern astronomy, the significance of constellations is no longer mythological, but practical. Astronomers use the term to describe an entire region of the sky and all the objects in that region.
Note that in the various examples we show of the famous constellation Orion, the view from the Northern hemisphere is depicted. But in the Southern hemisphere we see constellations upside-down, because we are "down under" as compared to the Northern hemisphere. Here are the two views of Orion compared.
Orion from 40 degrees Latitude North (left) and from 40 degrees Latitude South (right)
Images generated with Skymap Pro