A WordPress plugin is a software component used to extend the functionality and features of a website powered by the WordPress content management system (CMS). Plugins are used to add new features or modify existing functionality on WordPress sites and can be easily installed and managed by site owners, often without requiring any coding knowledge.

1. Enhancing Functionality: Plugins are used to increase the functionality of the site. For example, various functionalities can be added, such as a contact form, SEO tools, firewall, e-commerce features, social media integration.
2. Ease of Use: WordPress plugins are generally user-friendly and, in most cases, can be installed and configured with just a few clicks.
3. Customizability: Many plugins offer options and settings that can be adjusted according to the user's needs.
4. Wide Diversity: WordPress plugins come in a wide range, from simple functions to complex applications, and can fulfill almost any type of website need.
5. Community and Support: WordPress plugins are often supported by an active community of developers and users. These communities can help with resolving issues, developing new features and security updates.

WordPress plugins, https://wordpress.org/plugins/ can be downloaded from the official plugin directory or from various third-party providers. The security, performance and compatibility of each plugin may vary, so it is important to consider these factors when installing a plugin.