The difference between the installed fonts in the computer used to create a document and the computer used to display and print the document. Computers come with a standard set of fonts. In order to use a different font, the target computer has to have the matching font to render it accurately.
Prior to the PDF format, which solved this font incompatibility problem, people used the same Arial and Times New Roman fonts all the time because they were standard in most computers. The PDF format embeds the fonts from the source computer into the document itself and enables more text creativity (see
PDF). See
font.