Enharmonic notes are simply notes that have more than one name. Just as you might be known by not only your given name, but also by your nickname, so notes can have more than one name. The same is true for enharmonic chords — they can be known by multiple names as well. For example, the Db major chord sounds exactly the same as the C# major chord, but looks different on printed music, and has two different names: C# major and Db major.

Keys With Two Names — Chords With Two Names