PostScript fonts are based on the Adobe PostScript language. There are lots of font formats. Type 1 fonts, one of the PostScript formats, are presently widely used in desktop publishing. Type 1 fonts use a subset of the PostScript language. Type 1 font files consist of two files — a screen font with bitmap information for on-screen display and a file with outline information for printing the font. For commercial printing, both of the Type 1 font files must be included with the application file.
Due to differences in their structure, Mac and Windows PostScript Type 1 fonts are not cross-platform compatible.
In addition they also known as: PostScript fonts | PS fonts
Examples: “Each Windows Type 1 font will have a .pfm (Printer Font Metrics, your screen font) and a .pfb (Printer Font Binary, your printer font) file. The icon for both files is a dog-eared page with a lower case script a (for Adobe). On a Mac, the bitmap font icon appears as a dog-eared page with the letter A. The outline file icon appears as a letter A front of horizontal lines.”