To output, even if to a screen. If a hacker says that a program “printed a message”, he means this; if he refers to printing a file, he probably means it in the conventional sense of writing to a hardcopy device (compounds like ‘print job’ and ‘printout’, on the other hand, always refer to the latter). This very common term is likely a holdover from the days when printing terminals were the norm, perpetuated by programming language constructs like C's printf(3). See senses 1 and 2 of tty.