The question is asking which software is most widely used to view and explore text, pictures, and videos on the World Wide Web. Let's analyze each option to determine the correct answer.

1. Search Engine: A search engine is a system that helps users find specific content on the World Wide Web. It is not the tool for directly viewing and exploring web content but provides links to web pages.
2. Browser: A browser is a software application used to access information on the World Wide Web. It allows users to view text, pictures, videos, and other content from websites. Examples of web browsers include Google Chrome, Mozilla Firefox, and Safari.
3. Web Server: A web server is a dedicated computer where websites are hosted. It serves web pages upon request but is not directly used by end-users to view content.
4. Operating System: An operating system is system software that manages computer hardware and software resources; it is not used for browsing the web.

Based on the definitions, the correct answer should be Browser because it is the software that allows users to view and explore text, picture, and video content on the World Wide Web.