Probably better to think about it less as a term describing a physical device but more as a term describing a logical set of computing-based capabilities that a person can use to perform a set of desired activities. In that sense it means different things to different people, hence why an iPad - or Chromebook - may or may not be a "PC" replacement.
PC was actually a specific product believe it or not and we do have clear criterias as to what makes a PC and not. get ready, its Story time. back in the day, computers from different manufacturers werent cross compatible. everyone had different CPU`s, different firmware, different connectors, etc. a program written for one wouldnt run on another. in 1981 IBM released a computer model named "the IBM PC" that mostly ran DOS, you could pick 3 different OS`s but 96% chose DOS. it was built using mostly commercially available components to get it to market quickly, notably the 8088 cpu from intel. it was repair friendly and encouraged 3rd parties to make accessories for it. it also introduced BIOS and MBR as means of booting. it soon became the dominant computer for personal use and grew a big software library. Compaq came up with the idea of instead of trying to compete with the IBM PC. it would become it. Compaq reverse engineered the architecture and built a computer that could run the same software as the IBM PC. IBM didnt have enough patents on their IBM PC to stop them. soon other manufacturers followed suit and the personal computer industry had a common platform, dubbed the as the PC platform, also called the IBM PC compatible market.
this is how MS and Intel gained their monopoly. those IBM PC clones needed DOS and Intel CPU`s to run that huge PC software library they wanted. being IBM PC compatible became a must to be relevant in the PC industry so they followed Microsoft and Intel`s lead. IBM eventually became irrelevant after they failed their attempt to gain control over the market with OS/2. the IBM PC platform was redubbed as the Wintel platform and thats essentially what PC is defined as to this day. i think this is important history to know about when we discuss about what is and is not a PC, and important tech history in general.
today, we can classify a PC as any computer system that is:
-compatible with Microsoft Windows
-Uses industry standards like, DDR, PCI-E, USB, HDMI,
-Has a BIOS or its successsor, EFI
-uses Intel`s X86 instruction set
-Designed to be operated by a single user(eg, is not a server)
So iPads and ARM based Chromebooks are not PC`s in this sense. i personally like to use the term General Purpose Computer(GPC) when describing devices that are used for the same purposes that we use PC`s for today