Portable Compiled Format (PCF) is a bitmap font format used by X Window System in its core font system, and has been used for decades. PCF fonts are usually installed, by default, on most Unix-based operating systems, and are used in terminals such as xterm. PCF fonts replaced BDF due to a slight efficiency increase, however most applications have moved on to scalable fonts.
References
Portable Compiled Format Wikipedia(Text) CC BY-SA