The Jargon File is in the public domain, to be freely used, shared, and modified. Cite the File correctly, with a version number and date. Try to check with a maintainer before excerpting. These conventions are ways to cope with the fact that some of the File's material dates rapidly.
Helpful detail follows.
Please check the Jargon File Resource Page before quoting to make sure you have the latest, freshest version. This is good for your readers and helps the File's maintainers too. Of course, you want to cite the correct current version. The point of this practice is to clue in your readers when the quote might become dated.