FFI (Foreign Function Interface) is the bridge that allows a program in one language to invoke functions, use data types, and link libraries written in a different language.
It relies on a shared ABI (calling conventions, type layouts, name mangling) so both sides agree on how arguments and return values are passed and how memory is represented.
An ABI (Application Binary Interface) is the contract that lets separately compiled programs and libraries work together at the machine-code level.
It specifies details like function calling conventions, register usage, stack layout, how integers/floats/structs are represented in memory, name mangling, and how symbols are linked and loaded.