What does "frontend" refer to in web development?

In web development, the term "frontend" specifically refers to the client-side aspects of a website or web application that users can see and interact with directly. This includes elements such as the layout, design, and user interface features, which are built using technologies like HTML, CSS, and JavaScript. The frontend is focused on user experience and ensures that the presentation is visually appealing and functional, allowing users to engage effectively with the site.

When considering the other options, "backend services that process data and deliver content" pertains to the server-side of web applications, which handles data processing and storage but is not visible to the user. The "server-side infrastructure managing databases" is similarly related to backend operations, focusing on how data is stored and accessed on the server rather than user interaction. Lastly, "security protocols that protect user data" refers to measures taken to secure data, a critical aspect but not one that involves user-facing interactions. This distinction reinforces why the choice regarding client-side aspects is accurate in relating to the concept of "frontend" in web development.