PPC = PowerPC, referring to the processor found in Macs before 2006 known as 601, 603, 604, G3, G4, and G5.
These were made by Motorola and IBM to varying degrees. In spite of that fact, they are less compatible with IBM PC compatibles
than the newer Intel Macs.
Intel is not PPC, and PPC is not Intel.
If you have 10.6 or later Mac OS X installed, you don't have a PPC.
If you have Boot camp installed, you don't have PPC.
If you have 10.4.4 (including 10.4.10 and 10.4.11, but not 10.4.1) through 10.5.8 installed, you may have PPC, or you may not
as those were the only Mac OS X versions written for both CPU types.
Mac OS X 10.4.3 and earlier could only be installed on PPC Macs.
As a side note, to ease the migration from PowerPC to Intel, Apple offered an environment known as Rosetta in 10.4.4 through 10.6.8 allowing applications
developed for PowerPC to be used on Intel Macs. This environment is still available on newer operating systems with a virtualizaiton solution.
Here's how to identify iMacs visually. These two are PPC (PowerPC):
iMac G3s with Firewire ports can also be upgraded to 10.4.11. Those without Firewire could only be updated to 10.3.9.
See this image to determine if they have Firewire ports:
This one may be PPC, or Intel depending on the EMC# read off the bottom of the foot:
EMC# 2104, 2105, 2110, 2114, 2118, 2111, 2133, or 2134 are all Intel. Others are PPC and known as iMac G5.
This one is Intel: