These Base14 fonts are built-in into PDF and all viewers can display them. Using these fonts may decrease the size of the result file and make the processing faster, avoiding loading external fonts. However the fonts support only latin1 character set and you have to load external fonts if you need to use an other character set.
The Base14 fonts:
Courier
Courier-Bold
Courier-Oblique
Courier-BoldOblique
Helvetica
Helvetica-Bold
Helvetica-Oblique
Helvetica-BoldOblique
Times-Roman
Times-Bold
Times-Italic
Times-BoldItalic
Symbol
ZapfDingbats