What is PSR4? PSR4 – Proposal for Standard Request number 4

Why use? This is a standard using which allow the classes to be automatically discovered and loaded by following a convention for class namespace and file/directory naming.

Drupal 8 initialy used PSR0 but changed to PSR4.

We don’t have to use functions like require_once, include() and module_load,module_load_include function using this.

Each module has namespace that corresponds to its module name.