A process is an instance of a program in execution. A file is an object on the filesystem; beside regular file with plain text or binary content; it could also be a directory, a symbolic link, a device-special file, a named pipe, or a (Unix-domain) socket.
The Unix design philosophy abstracts peripheral devices (such as the keyboard, monitor, mouse, a sensor, and touchscreen) as files – what it calls device files. By doing this, Unix allows the application programmer to conveniently ignore the details and just treat (peripheral) devices as though they are ordinary disk files.
The kernel provides a layer to handle this very abstraction – it's called the Virtual Filesystem Switch ...
