There are three types of fonts you need to be aware of: TrueType, PostScript and OpenType. They are stored in different directories on the different operating systems.
OpenType fonts are cross-platform compatible making it easier to share files across operating systems. Font management is simpler since there is just one file involved. An OpenType font file contains all the outline, metric and bitmap data in one file. It can contain TrueType (.ttf extension) or PostScript (.otf extension) font data and uses ATM to render the font on-screen. Adobe® InDesign® and Adobe® Photoshop® support OpenType which allows them to use the expanded character sets and layout features.
Truetype fonts only require one file to be submitted but a separate file needs to be submitted for each instance of the font. For example, a different file is needed for normal, bold, italic, bold italic, etc. TrueType typefaces are generally intended for business office use and can be less reliable for publishing applications. Only use TrueType typefaces when the typeface is unavailable in PostScript format.
There are generally two main components to PostScript typefaces. The first file contains the actual PostScript typeface itself and is often called the “binary” or “printer” file. The second file contains the typeface’s complete name, the spacing characteristics (font metrics) and information to help the computer display the typeface on the screen and for printing the font. Both files must be submitted.