A file in your typical UNIX home directory that lists what Usenet newsgroups you have subscribed to. The file is shared by most "normal" newsreaders.
The format is fairly simple. For example, here are some lines from my .newsrc (it has total of 22 at the time, not all included):
The lines have group names, then a colon, and then a list of articles that you have read (or at least marked read), in format "a-b,c-d,e-f..."
The ':' means that you have subscribed the group; If it's a '!' it means the group is not subscribed. However, now that there are zillions and zillions of newsgroups, some newsreaders conserve space and just drop the groups that you haven't subscribed to from the list.
Some newsreaders use different name for this file (for example, slrn uses ~/.jnewsrc as the default) and some store auxiliary information to other file (Gnus uses ~/.newsrc.eld).