n. 1. A file containing a listing (e.g., assembly listing) or a transcript, esp. a file containing a transcript of all or part of a login session. (The idea was that the paper for such listings was essentially good only for wallpaper, as evidenced at Stanford, where it was used to cover windows.) Now rare, esp. since other systems have developed other terms for it (e.g., PHOTO on TWENEX). However, the UNIX world doesn't have an equivalent term, so perhaps wallpaper will take hold there. The term probably originated on ITS, where the commands to begin and end transcript files were ':WALBEG' and ':WALEND', with default file 'WALL PAPER' (the space was a path delimiter).
2. The background pattern used on graphical workstations (this is techspeak under the 'Windows' graphical user interface to MS-DOS).
3. 'wallpaper file' n. The file that contains the wallpaper information before it is actually printed on paper. (Even if you don't intend ever to produce a real paper copy of the file, it is still called a wallpaper file.)