Extensions are tools or add-ons that enhance the functionality of software applications, particularly web browsers like Google Chrome or Mozilla Firefox. They allow users to customize their browsing experience by adding features such as ad blockers, password managers, or productivity tools. By installing extensions, users can tailor their online activities to better suit their needs. In addition to web browsers, extensions can also refer to features in software programs like Microsoft Word or Adobe Photoshop. These extensions can provide additional templates, filters, or editing tools, making it easier for users to accomplish specific tasks. Overall, extensions help improve efficiency and user experience across various platforms.