What is Zephir in Phalcon?

Zephir – Ze(nd Engine) Ph(p) I(nt)r(mediate) – is a high-level language that eases the creation and maintainability of extensions for PHP. Zephir extensions are exported to C code that can be compiled and optimized by major C compilers such as gcc/clang/vc++. Functionality is exposed to the PHP language

source (https://github.com/phalcon/zephir)