$ # K bulletin board system (BBS)

An electronic system in which users participate in discussions by leaving public messages for each other.  Most BBS's are run on personal computers and are accessible only by dialup modem.  Many have additional features, such as online games and a file repository.  

Usenet News is not a BBS in the usual sense of the word, but it provides the messaging features of a BBS on a much grander scale than found on any existing BBS.
$ # K Usenet

A loosely-organized network of perhaps 100,000 computers worldwide.  These computers are linked in a number of ways, including modem and TCP/IP.  The best known service provided by Usenet is Usenet News.

# $ K article

A message written by a Usenet News user and posted to the network.  Articles are similar to electronic mail messages, but are not private.  They are intended to be seen by potentially hundreds of thousands of people.  Also called "postings".

# $ K newsgroup

A collection of articles on a given topic.  When you write an article, you specify to which group or groups it should be sent.  

Each newsgroup has a hierarchical name which suggests the topic of that group.  Names consist of several words separated by periods.  The first word in the newsgroup name states the general category covered by that group, the second, a subcategory of that general category, and so on.

For instance, the newsgroups sci.chem and sci.math are scientifically-oriented groups which are dedicated to chemistry and mathematics, respectively.  soc.culture.indian is sociologically-oriented group devoted to the culture of India, and so on.

# $ K news reader

A computer program through which you interact with the Usenet News system.  News readers allow you to select and read articles written by others, and to write and post articles of your own.  

A number of news readers have been written over the years, many of them for computers running the Unix operating system.  The best-known news readers are probably rn, vn, nn, and xrn.
# $ K posting

The act of sending an article to the Usenet network, to be seen by potentially hundreds of thousands of individuals.

Also, a synonym for "article".
# $ K header

A series of lines at the beginning of an article or electronic mail message that contain such information as the article's or message's author, its subject, its date and time of transmission, and so on.  The header is separated from the actual text of the article or message by a blank line.
# $ K electronic mail message

A message sent privately to one or more explicitly-named individuals.  Electronic mail is not provided by Usenet News per se; electronic mail messages are not the same as news articles.  However, many news readers provide the capability of sending (but usually not receiving) electronic mail because it is often desirable to respond privately to an article.
# $ K news server

A computer that runs special software to exchange news articles with other computers in the Usenet network, and makes these articles available to local users.  News readers require access to a news server, but they do not require you to have an account on a news server.

# $ definition

A type of hypertext link in Microsoft Help.  A definition is a (usually) brief description of a term.  Definitions appear when you press and hold the mouse button on a term that appears in Help as green text marked with a dotted underline.  

The description disappears as soon as you release the mouse button.  
Hence, it is not possible to access hypertext links within a definition.  Some definitions contain hypertext links, however, because they are also available as cross-references.  It is usually possible to reference a definition as a cross-reference via the Help Search button.
# $ K Cross Reference

A type of hypertext link in Microsoft Help.  A cross reference is a topic that appears in the Help window when you click on a term that appears in Help as green solid underlined text.