An etching is an original piece of art.
Whereas posters, art prints and so-called "limited editions" only reproduce an existing original piece of art, the etching is a unique art form. It is pretty hard for the general public to see the difference between an original graphic print and a commercially motivated reproduction as the latter are numbered and signed as well. However, the difference is that in an original graphic print, the artist has worked on the copperplates himself, employing combinations of etching, aquatint, drypoint and/or mezzotint techniques.
So with an etching, the artist uses a variety of tools to put holes, scratches, and hollows into the perfectly polished copperplate.
He then covers the plate with oil paint. He takes off any excess paint with the palm of his hand, and then covers the plate with a soaked sheet of hand-made paper and runs it through his press.
The motif is directly scratched into the plate or plates, i.e. there is no other original that is simply reproduced. The graphic print produced as described is the true work of art.