The basic design of a microprocessor. It includes the design of the instruction pipeline and execution techniques, number and style of on-board caches and caching techniques and type and speed of the system bus. The microarchitecture also defines the process technology and base materials used for the construction of transistors, electronic components and interconnects.
Microarchitecture Vs. Architecture
The microarchitecture is the very specific design of a microprocessor, while a chip's architecture refers to the broader family of chips. For example, Intel's x86 family, known as "IA-32," is the architecture, while P5, P6, NetBurst, etc. are microarchitectures that were implemented for IA-32. See pipeline
Starting with the first Pentium chip, Intel has had numerous microarchitectures, all part of the x86 family.