Ground Controls->Non_PDF->Fonts->Type
These Ground Controls deal with actual font types.
TrueType® - This Ground Control will trigger if a font is detected as a TrueType font. With the advent of OpenType, TrueType fonts can now be wrapped in an OpenType wrapper. Flightcheck will report these OpenType fonts as TrueType.
City/System Fonts - City named fonts like Geneva and Chicago will trigger this Ground Control. This is a holdover from the OS9 days when fonts with city names caused jaggy type to be imaged on many output devices.
Multiple Masters - Multiple Master fonts are fonts that can be morphed into other shapes. The most common Multiple Master fonts are the ones shipped with Adobe Acrobat which are used to display non-embedded or subsetted fonts that are missing in the PDF file. From a preflight perspective Multiple Master fonts used to cause many output problems from the RIP. Depending on your workflow, Multiple Master fonts may be good or bad, you will need to communicate with your printer as to whether these type of fonts cause issues through their workflow.
Non-Adobe® - There are many great type foundries out there. In the days of yesteryear, fonts that were not from Adobe used to cause issues with many RIPs. In todays world this is not as common.
OpenType® - OpenType fonts are designed to be cross platform (Mac and Win). OpenType fonts are different than older font tecnologies in that they have the ability to contain up to 65,000 glyphs within a single font. These additional characters could be alternate swash characters or different languages. The newer RIPs should be able to handle OpenType fonts. From a Printer's perspective OpenType fonts are good in that they are a single font file unike Postscript fonts that have a bitmap portion of the font (Screen Font) and a printer portion of the font (Printer Font).