What is an architecture license?
An architecture license is a license to use an instruction set architecture (ISA).
This means that the licensee is licensed to create a processor implementation of the ISA providing it is compliant. This leaves the licensee free to choose microarchitectural details such as the number of pipeline stages, number of issues, whether in-order or out-of-order execution among other. The licensee is responsible for verifying the implementation of the core that uses the ISA.
Historically architectural licenses have been mainly for proprietary ISAs. They have typically had very large license fees. With RISC-V the ISA is licensed by RISC-V International without a fee.