The Arm Architecture is the bedrock of all that Arm does, and the foundation on which all CPU products are formed.
What we mean by architecture is the contract between the hardware & the software assigning rights and responsibilities between those two parties. This defines how compatible hardware behaves for correctly written software and is the very essence of the portability guarantee of Arm.
The architecture defines the basic instruction set, and the exception and memory model that are relied upon by the operating system and hypervisor - in effect, the architecture defines what the CPU must do, but actually says very little about how it does it.
The Micro-architecture and Implementation of the CPU sit on top of the architecture, and determine how it meets the architectural contract, and defines the processor’s power, performance and area by determining the pipeline length, levels of cache etc.