Binary files include data which is not plain text: they may be programs, pictures, sound files, zip files, word processor documents, etc. Because binaries require special decoding, often take a long time to download and can potentially harbour viruses, they are very unwelcome in most newsgroups, except those that include the word binaries in their name. Posting a binary to a non-binary newsgroup is a breach of Demon's AUP (Acceptable Use Policy) for news. A discussion about this (and other) types of abuse of the Internet can be found at:

http://www.demon.net/helpdesk/aup/discussion-news.shtml

One point needs particular care. If you need to quote a text file in an article you write (perhaps part of a log file, or a word processed document) it is usually best to "cut and paste" the text into your article to ensure that it really is text. Some newsreaders offer an option to insert a file, but this needs caution, since the insertion may be encoded as an 8-bit binary file.

Posts using HTML are not binaries, but they are unpopular in most newsgroups.

If you subscribe to a binaries group, set your newsreader to download just headers ("browse" mode) to avoid the very long download times needed by binary files. Later you can explicitly request the bodies of articles that look, from their Subject lines, to be of interest.