What is the plugin?

component or a code template used to do some functionalists like executing jobs, reading files ..etc.

Plug-in (computing), a piece of software which enhances another software application and usually cannot be run independently

A plugin is used to extend the functionality of an existing system.
For example, the Flash plugin enables Firefox to display Adobe Flash content.

Plug-in (or plugin, extension) is a software component that adds a specific feature to an existing software application.
When an application supports plug-ins, it enables customization.
The common examples are the plug-ins used in web browsers to add new features such as search-engines, virus scanners, or the ability to utilize a new file type such as a new video format.

A plug-in is a set of software components that adds specific capabilities to a larger software application, it can be a web application plug-in or mobile application plug-in , etc

plugin is things help you to short the way on you when you make a website or design something

when you install plugin like jquery slideshow or sickbox you can click on it from insert menu and then it's install automatic in my site without typing eny code and then u can change the height , width , others things like u want.

A plugin extends jQuery directly and may or may not have a visual component.
like widget that have visual apperance Plugins are functions that do something to your website.
They could serve a back-end purpose and never be visible to you or the public.
Plugins allow you to set various parameter & values to customize the settings the one you using in your website