The result is not standard PHP and cannot be read by humans without significant effort.

: To run these files, a server must have the ionCube Loader installed, which decrypts and executes the bytecode at runtime. The "Online Decoding" Landscape

Ioncube is an for PHP. It takes human-readable PHP source code and converts it into a binary format (bytecode) that the server cannot understand unless a special loader (the ionCube Loader) is installed. It is not encryption in the traditional sense; it is compilation into a low-level intermediate representation.