Etching is the process of using strong acid or mordant to cut into the unprotected parts of a metal surface to create a design in intaglio in the metal (the original process—in modern manufacturing other chemicals may be used on other types of material). As an intaglio method of printmaking, it is, along with engraving, the most important technique for old master prints, and remains in wide use today.
Read more about Etching: Basic Method, Modern Technique in Detail, Types of Metal Plates, Industrial Uses, Printing, Faults, "Etchings" Euphemism