"C'est un dictionnaire en ligne." Don't understand? Here's a translation for you: "This is an online dictionary." A translation is the written or verbal rewording of something from one language into another that keeps the same meaning.
A translation doesn't have to be strictly from one language to another; it can be a rewording that makes something easier to understand or less technical in nature, as suggested by the common phrase, "Can you translate that into plain English?" If what is translated takes a written form, as in a book, for example, then the object itself is called a translation.