It is an arbitrary subroutine, and can do whatever you need. This is easier to understand with an example. That time is long past. Usenet has grown to thousands of newsgroups carrying millions of articles per day. Accessing usenet requires powerful tools, and even then, the best anyone can hope for is to see a tiny fraction of the traffic.
Many people access usenet through a newsreader.
It reads all the articles in the newsgroup, and all its subgroups, and prints any lines that contain the string. Depending on the size of the newsgroup, the program can take a long time to run. Remember, Laziness is one of the principle virtues of a programmer.