In case you are wanting the history. IBM actually coined the term PC with their IBM Personal Computers
At the time most computing platforms were incompatible. Software written for a commodore computer wouldn’t work with an apple computer wouldn’t work with an IBM PC.
The IBM PC was popular enough though that people started building “pc compatible” machines. A very popular configuration for this was intel chips with Microsoft DOS. While these machines started out as “pc compatible” after a while the IBM PC wasn’t a big deal anymore so saying “we are compatible with a machine released in 1981” just slowly morphed into “it’s a PC” as shorthand for “intel chipset with Microsoft OS”
Now why didn’t apple get the pc moniker? At the time when the IBM PC launched apple was actively building and selling their own computers and weren’t interested in making them IBM PC clones so they never went out and marketed themselves as “pc compatible” because for the most part they were not.
Nowadays I mostly think of it in regards to how much control you have over the hardware. If you can Ship of Theseus your way to a completely different machine with completely different specs, that's a PC to me. If you're stuck with what you paid for, then it's something else. A Mac Mini is not a PC in my book, but a Hackintosh is even though it's the same OS and general hardware architecture.