Plugin refers to software applications that are programmed using interfaces to extend the functionality of other software.
If a software product is used by a lot of people, there will soon be great demand for additional features. Therefore, more and more software providers build interfaces that allow the programming of new features and to connect with the software. Thus, a somewhat limited software is transformed into an all-rounder for the most diverse requirements.
The terms plugin and add-on are often used interchangeably. However, this is strictly speaking incorrect. A plugin is an extension of a software, which can also function without the actual main program. An add-on on the other hand, extends software, but cannot run without it and is therefore only useful in conjunction with the main program.
A classic example are browser add-ons. Modern browsers such as Mozilla Firefox, Google Chrome or Internet Explorer are designed so that they can be expanded through add-ons any time. Thus, for example, their security can be upgraded, the management of bookmarks or searching the web can be simplified, and the display of the browser can be adjusted.
Plugins exist for certain image editing programs. Typical representatives of this category are Photoshop, Gimp, and IrfanView. Through a plugin, graphics filters can be added or the processing ability for certain graphic formats can be supplemented, for example. Also vector graphics applications or 3D software is available. Plugins are also used in the following software products:
Content management systems can be expanded almost infinitely through plugins. There are about 27,000 plugins available just for WordPress. Joomla or TYPO3 likewise have large plugin directories. These extensions can perform the following functions, for example:
Open source shop systems also get extended with plugins. Typical examples of module-based shop systems are Magento, xt:Commerce, and Shopware. The software manufacturers offer large marketplaces with hundreds or even thousands of extensions that are partly provided by the manufacturer. Many of these modules are however programmed by third parties for free or for purchase.
The advantage of plugins is clearly in the enhanced functionality without having to purchase any additional software. Such extensions are very often available free of charge. The usually simple and mostly automated installation is advantageous as well. Access to the plug-in happens directly through the navigation of the main software.
Plugins can pose a problem when programmed by a third party and available for download. In this case there is often no control as to whether the specified functionality is provided without restriction. There can be no guarantee that the software has no security vulnerabilities.
For search engine optimization, plugins have significance insofar as particular browsers, content management systems, and shop systems can be extended with SEO functionalities. With browser add-ons and toolbars, important indicators such as the visibility index or backlinks can be tracked. They help with keyword research, analyze source code or show information about Whois of a website.
In CMSs, plugins can help to handle the most important on-page optimization actions, for example, updating of metadata, images optimization, caching, and internal linking. Using modules, shop systems can be expanded with rich snippets, canonical tags, blog functions, sitemaps, friendly URLs, and many more SEO functionality. Plugins do not offer any information that could not be obtained through other tools, but since they are usually free of charge and get the latest information directly to the right place, they can greatly facilitate the work of search engine optimizers.