A plugin is a set of functions dedicated to work as an independent solution, while extending or adding new features to WordPress. In WordPress, plugins are similar to the Apps we use in iOS and Android. We have the ability to use or remove any plugin without affecting WordPress's core features. Also, plugins allow us to separate independent features into their own plugins, making them easier to maintain. The wordpress.org plugin base has over 50,000 free plugins, and sometimes you don't have to develop anything for WordPress websites. You can just use a number of plugins and integrate them properly to build advanced features.
The role of plugins is vital for the development of a site. In Chapter 3, Designing Flexible Frontends with Theme Development, we discussed the role of a theme, and the features beyond the scope of a theme...