Orwell wrote:
Before the Intel switch, Apple used PowerPC processors. Macs are PCs.
In the strictest sense of the term, PC stands for Personal Computer, this much as already been said.
Thing is, the term "Personal Computer" came about in the 1980s when computers that could (ZOMG!) fit on your desk (instead of taking up entire rooms) came into existence soon after the invention of the transistor... that meant that each person could have their very own *personal* computer, instead of having to share a mainframe that was at some university with a bunch of other researchers...
So, technically, everything that has a processor in it (i.e. a machine can perform "computations"), and is small and cheap enough that everyone can have their own (should they choose to purchase), is a "personal computer". That means that iPods and newer cell phones are PCs just as the large towers are... And yes, any machine made with the Macintosh label fits said definition...
In a more historical context, however, the term "PC" came to apply to the concept of "100% IBM compatible PC" (back in the day when IBM was the forefront of PC hardware development and manufacturing)... That's where the idea of PPC, which was not an IBM compatible architecture, was somehow *not* a PC, and Apple's marketing division (and by extension, fanboys) has clung to this 1980s fantasy ever since...