Joomla Plug-In-Development:

Joomla Plug-in serve a wide variety of purposes.  As joomla modules enhance the presentation of the final output of the Web site, plugins will enhance the data and can also provide additional, installable functionality

Plug-ins is event driven units of code. So if you need something to happen after someone logs in then we can create a plug-in. plug-ins also are tools to help bridge gaps in the Joomla framework. Components and modules sometimes call plug-ins inside them, for instance, Joomla editors are plug-ins. If you need something to happen after a Joomla event in your website or you need something that a component or module cannot do then let us create a plug-in for your website.

There are number of different plug ins in Joomla development they are listed below they are:
•    Authentication
•    Content
•    Editors
•    Editors-xtd
•    Search
•    System
•    User
•    Xmlrpc

While a plug-in can have any number of files, there are two you need as a minimum and there are specific naming conventions you must follow.  Before we look at the files, we must decide what sort of plug-in we are going to create.  It must either fall under one of the built-in types (authentication, content, editors, editors-xtd, search, system, user or xmlrpc) or your can create your own type by adding a new folder under /plugins.