difference between extension and plugin?

Question

what is the actual difference between a extension and plugin?

eg. is phplivex a extension or plugin?

i have to know in which folder i should put it in

Answer 1

According to the website, PHPLiveX is a php ajax library and framework to use php with ajax, so it is neither an extension nor a plugin.*

Extensions in PHP are usually C libraries that PHP can be compiled with or that can be enabled in php.ini that provide a certain functionality. For instance cURL is an extension that lets you do HTTP Request.

The term Plugin has no definite meaning in PHP. Existing userland libraries and frameworks can be enhanced through plugins to add functionality to them. For instance, in Zend Framework, you can write custom plugins for Zend_Controller to add custom behavior at runtime.