the phrase "dead trees" refers to paper.

A saying from the Jargon File is that "You can't grep dead trees", which comes from the Unix command , which searches the contents of text files. This means that there is an advantage to keeping documents in digital form, rather than on paper, so that they can be more easily searched for specific contents. A similar entry in the Jargon File is "tree-killer", which may refer to either a printer or a person