RISC-V is an instruction set architecture that is freely available for use. That is, it specifies the instructions and instruction encodings used by a CPU, like

RISC-V is an instruction set architecture that is freely available for use. That is, it specifies the instructions and instruction encodings used by a CPU, like x86 and ARM. Unlike x86 and ARM, you don't need to license the ISA to create cores implementing it. RISC-V cores are not from a specific manufacturer.