Acronym for Personal Computer, an IBM trademark.
The idea that everyone would have their own machine was once a strange dream. Back then, people had a terminal connected to a larger machine shared among many users. The world turned, and the computer industry was forever changed.
IBM trademarked the term and specialised it to mean a x86 machine running DOS. This later evolved into WinTel. This leads to great confusion when pedants (like StuartYeates) refer to AppleMacintosh machines as PCs. LawrenceDoliveiro also claims to be such a pedant, and proposes the term MicrosoftCompatible to clarify what kind of PC is meant.