Definitions for KILL FILE
A file in which individual users of newsgroups can ignore postings by certain other users, or postings that match certain criteria
The New Hacker's Dictionary
[Usenet; very common] (alt.: KILL file) Per-user file(s) used by some Usenet reading programs (originally Larry Wall's rn(1)) to discard summarily (without presenting for reading) articles matching some particularly uninteresting (or unwanted) patterns of subject, author, or other header lines. Thus to add a person (or subject) to one's kill file is to arrange for that person to be ignored by one's newsreader in future. By extension, it may be used for a decision to ignore the person or subject in other media. See also plonk.