Interface between source program and target program?

The source program is a kind of computer code. It will conform to a certain grammar, and after being compiled or interpreted by a compiler, it will generate executable files or components with certain functions, or it can be some kind of interface. Programs written in source languages such as fortran and basic. The source language refers to a language that can output another language, and the language it produces is called the target language. For computer operation, the program written in the source language must be compiled into the target program. The compiler acts as an interface between them.