"My voice brought them out of the book." -Mo
A Silvertonge is a person that can bring characters, things, and beings, out of a book, simply by reading it aloud. Dustfinger refers to Mo simply as "Silvertongue" when he shows up at Mo's house at the beginning of Inkheart.
Silvertongues named in the books are Mortimer Folchart (Mo), Meggie Folchart, Darius and Orpheus. However, there may be unnamed Silvertongues elsewhere in the Inkworld.
One downfall to the Silvertongue's unique talent, is that for every character that comes out of a book, someone from our world must go in. Mo realizes he is a Silvertongue when he reads out Capricorn, Basta, Dustfinger, and Gwin. Sadly, Resa and their two cats, who were asleep on Resa's lap, went into the Inkworld.