CLI languages are computer programming languages that are used to produce libraries and programs that conform to the Common Language Infrastructure (CLI) specifications. With some notable exceptions, most CLI languages compile entirely to the Common Intermediate Language (CIL), an intermediate language that can be executed using the Common Language Runtime, implemented by .NET Framework, .NET Core, and Mono. Some of these languages also require the Dynamic Language Runtime (DLR).
As the program is being executed, the CIL code is just-in-time compiled (and cached) to the machine code appropriate for the architecture on which the program is running. This step can be omitted manually by caching at an earlier stage using an "ahead of time" compiler such as Microsoft's ngen.exe and Mono's "-aot" option.