Another word for filename, most commonly used in the context of a Unix filesystem. "Filename" can refer to just the last component of the path (i.e., containing no directory names or slashes), whereas "pathname" usually implies that a list of subdirectories under which the file lives are also included.

Pathnames can be relative to the current directory--for example, porn/fist.jpg--or may be "full pathnames" (also called an "absolute pathname")--for example, /home/jason/porn/fist.jpg. The difference is that the latter gives a complete description of where the file is found, from the root directory downwards.