ZDNet:

Apple Silicon is the phrase Apple presently uses to describe its own processor production, beginning last June with Apple’s announcement of the replacement of its x86 Mac processor line. In its place, in Mac laptop units that are reportedly already shipping, will be a new system-on-a-chip called A12Z, code-named “Bionic,” produced by Apple using the 64-bit instruction set licensed to it by Arm Holdings. Again, Arm is not the manufacturer but the designer of the processing cores and other on-chip parts. In this case, Arm isn’t the designer either, but the producer of the instruction set around which Apple makes its original design.

This sums up why calling them Arm Macs would be wrong.

Also, this interesting explanation about the differences between X86 and Arm:

The maker of an Intel- or AMD-based x86 computer does not design nor does it own any portion of the intellectual property for the CPU. It also cannot reproduce x86 IP for its own purposes. “Intel Inside” is a seal certifying a license for the device manufacturer to build a machine around Intel’s processor. An Arm-based device may be designed to incorporate the processor, perhaps even making adaptations to its architecture and functionality. For that reason, rather than a “central processing unit” (CPU), an Arm processor is instead called a system-on-a-chip (SoC). Much of the functionality of the device may be fabricated onto the chip itself, cohabiting the die with Arm’s exclusive cores, rather than built around the chip in separate processors, accelerators, or expansions.

As a result, a device run by an Arm processor, such as one of the Cortex series, is a different order of machine from one run by an Intel Xeon or an AMD Epyc. It means something quite different to be an original device based around an Arm chip. Most importantly from a manufacturer’s perspective, it means a somewhat different, and hopefully more manageable, supply chain. Since Arm has no interest in marketing itself to end-users, you don’t typically hear much about “Arm Inside.”