Copilot+ PC is Microsoft's label for Windows 11 PCs with an NPU that can run at more than 40 TOPS (trillion operations per second), which many of the newer Windows AI features require. Other requirements (RAM, storage): TBD; see Microsoft's developer guide: Microsoft Learn: Copilot+ PCs developer guide.
A Copilot+ PC is not necessarily good at running large open models; that depends on GPU memory or unified memory. See what is an AI PC.