Duplicate fonts are fonts that are exactly the same font but in different suitcase files or folders.
Details
Duplicate fonts can be either a PostScript font, Bitmap font, or TrueType font. FontDoctor will find (or "match") duplicate fonts, even of the font files are in different suitcases. Duplicate copies of the same font should never be opened by the System at the same time as this will create obvious confusion.
Solution
FontDoctor will move duplicated fonts to the Moved Fonts folder.