what is the defination of modules,plugin and components in joomla?and mainly explain and distinguish plug in and components.because i confuse both of you?
I strongly recommend you Google, Bing or whatever search engine you're comfortable with. Here is one link I found just by doing a web search: http://www.eboga.org/cms/joomla/how-to-extend-oomla-componets-modules-or-plug-in.html Modules, plugins and components are collectively referred to as extensions. An extension is third-party code (meaning that it is not part of Joomla core) that is installed within Joomla via the administrator. Each type of extension serves a specific purpose and has its own set of rules. The trick is to find the documentation that best explains it in terms you can understand. To anyone who wants to use Joomla (or any other such package), I strongly encourage you to read, read, read and then read some more. It may turn out that the solution you may think you need is in fact overkill or otherwise not quite the right fit for you. A few days of research will save you long-term headache, trust me.
plugins: effect the behavior of the site(how the site reacts to content,code you insert,etc.). components: addons that add additional applications to the site. modules: addons the can add additional features, but are only displayed through the module positions on the site.
i pretty much agree with Rodder7. my definitions as follows: Components are applications like file manager, xmap, backup, polls, etc... Plugins adds site fuctionality like SEF, how images behave (lightbox effect), SEO Modules are position related. So a poll is a component but you can use the Module to place it on certain pages like only the front page, or all pages. Some act very similar to plugins since I have one module that pulls latest posts from PHPBB and places them on the front page.