III. Conveying defamatory matter to others
Under the law of defamation, publication is the communication or making known by one person (the publisher) to another (the third party) of defamatory matters about and concerning the person defamed. It is not confined in printing and distribution of books/newspapers/magazines. If the words complained of have been told/disclosed/ disseminated (in written or oral form) to a third party, those words are considered to have been "published". To establish a claim for defamation, the plaintiff has to prove publication of the defamatory words by the defendant.
Suppose that there are only 3 persons involved in a case. If Mr. A published something defaming Mr. B to Mr. C, then Mr. A (i.e. the publisher) may be liable for defamation. The publication does not need to be made to a group of people (although the level of damage would be much lower if the defamatory matter is only published to a single person).