C-p and C-n (aka Ctrl-P and Ctrl-N) are the Emacs-style keybindings for previous (line) and next (line), very commonly encountered on the command line and in terminal applications. For example, most shells can use this in addition to up-arrow and down-arrow to cycle thru command history. Many, many more examples exist of applications (not just terminal-based, there are plenty of GUI apps too) that use this convention, as well as other Emacs-style keybindings (e.g. C-a for beginning of line, C-e for end of line).
