Section 47 is the reason a great many apparently defamatory statements produce no claim. It lists the publications that are privileged, and because § 45 and § 46 define libel and slander as "false and unprivileged", a privileged statement is not defamation at all rather than defamation with an excuse.
Subdivision (b) is the litigation privilege and it is the broadest: statements made in a legislative proceeding, a judicial proceeding, any other official proceeding authorised by law, or in the initiation or course of a reviewable proceeding. It covers pleadings, declarations, complaints to authorities and communications preparatory to litigation, and it is absolute — malice does not defeat it. The subdivision then sets out its own narrow exceptions: certain unverified allegations about a non-party in a marital dissolution or separation, communications furthering the destruction or alteration of physical evidence, communications concealing the existence of an insurance policy, a recorded lis pendens not identifying a qualifying filed action, and a knowingly false report to a law enforcement agency that someone has committed a crime.
Subdivision (c) is the common interest privilege and it is conditional: a communication without malice to a person interested in it, by one who is also interested, or who stands in a relation affording reasonable ground to suppose the motive innocent, or who was asked by the interested person for the information. The subdivision expressly extends to a former or current employer answering, on request and without malice and on credible evidence, about a job applicant's performance or qualifications, and to complaints of sexual harassment made without malice on credible evidence. Because subdivision (c) falls away where there is malice, most fights about it are fights about motive. Whether a statement is privileged, and under which subdivision, is one of the first questions a lawyer will look at.