[ from catenate via UNIX cat(1) ]
vt. 1. [techspeak] To spew an entire file to the screen or some other output sink without pause.
Among UNIX fans, cat(1) is considered an excellent example of user-interface design, because it outputs the file contents without such verbosity as spacing or headers between the files, and because it does not require the files to consist of lines of text, but works with any sort of data.
Among UNIX-haters, cat(1) is considered the canonical example of *bad* user-interface design. This because it is more often used to blast a file to standard output than to concatenate two files. The name cat for the former operation is just as unintuitive as, say, LISP's cdr.
Of such oppositions are holy wars made...