An unflattering, mostly pejorative word for personal computer. Usually refers specifically to the IBM compatible x86 machines that are so common these days, though some Sun, DEC, SGI or HP partisans use it to refer to Macintosh and Amiga systems as well.
What exactly is meant by PeeCee varies somewhat depending on who's saying it. Mac afficionados typically mean any sort of x86 machine, usually including AMD64 systems too, though with the advent of the Intel Mac, it tends to mean a machine running Windows. UNIX partisans usually use it in much the same sense, though some x86 machines running some breed of UNIX might be considered proper workstations instead. The common thread is a sort of disdain for cheap, commodity software and hardware, with the implication, whether correct or not, that it must be inferior in order to be so inexpensive. In the days of the m68k and PowerPC Macintosh, the venom was often directed at the hardware. This is usually what Sun and SGI partisans rant about, too - and it must be admitted that prior to the 486 and the introduction of PCI, many things about x86 systems were quite losing.
Nowadays, the vitriol is directed against Microsoft Windows with greater frequency than against the hardware itself, and even the high-end UNIX workstation partisans have been forced to admit that x86 hardware, at least in its high-spec incarnation, has caught up. This form is sometimes underscored quite strongly - many UNIX fans are not hesitant to deride a newer x86 system running Windows as a 'lousy PeeCee', while an older, lower-spec x86 running, for example, OpenBSD gets called a 'workstation' or 'server' without reservation.