What is PHP and how is it typically used in web application development?

Introduction / Context:
PHP has been one of the most widely used languages for building dynamic web applications. It powers popular platforms like WordPress, Drupal, and many custom web applications. Interviewers often start with a basic question about what PHP is and how it is used to ensure that candidates understand its role in the web application stack and can distinguish it from client side languages and other technologies.

Given Data / Assumptions:

• We are discussing PHP in the context of web development.
• PHP executes on the server and generates HTML or other content sent to the client.
• PHP can connect to databases, work with files, and interact with many services.
• The question is asking for a high level definition and typical use cases.

Concept / Approach:
PHP (Hypertext Preprocessor) is a server side scripting language designed for web development but also suitable for general purpose scripting. It is embedded into HTML, where PHP code is processed on the server to produce dynamic content. Because it runs on the server, PHP can interact with databases, perform authentication, process form submissions, and integrate with APIs and other backend services. The browser receives only the generated output (usually HTML, JSON, or XML), not the PHP code itself. PHP is open source, cross platform, and widely supported by hosting providers, which contributed to its popularity.

Step-by-Step Solution:
Step 1: Define PHP as a server-side scripting language interpreted by the PHP engine running on a web server. Step 2: Explain that PHP files can contain a mix of HTML and PHP code, where the PHP sections are executed on the server to produce dynamic content. Step 3: Describe common tasks handled by PHP such as processing web forms, managing user sessions, authenticating users, and interacting with databases like MySQL. Step 4: Note that PHP can generate not only HTML but also JSON, XML, and binary content for APIs and file downloads. Step 5: Emphasize that PHP is open-source, runs on many platforms, and is integrated into many hosting stacks (LAMP, WAMP), making it a popular choice for web development.

Verification / Alternative check:
Documentation and tutorials confirm that PHP is executed by the server and that browsers see only the resulting markup or data. Installing PHP alongside Apache or Nginx and loading a .php file demonstrates that PHP code runs on the server, accessing databases and files as needed, while the browser receives generated content. This behaviour distinguishes PHP from languages like JavaScript, which traditionally ran only in the browser (though JavaScript now also has server side runtimes such as Node.js).

Why Other Options Are Wrong:
Option B is incorrect because PHP does not run natively in the browser; it is not a client side language in the traditional sense. Option C is wrong because PHP is not an operating system; it is an interpreter that runs on top of operating systems like Linux or Windows. Option D incorrectly describes PHP as a database engine; while PHP can communicate with databases, it does not replace them and is not itself a database system.

Common Pitfalls:
A common misunderstanding is to blur the roles of PHP and JavaScript, leading to confusion about what code runs where. Another pitfall is mixing PHP logic directly into large HTML templates without structure, making code hard to maintain. Modern PHP development often uses frameworks (such as Laravel or Symfony) and templating engines to organize code cleanly, separating business logic from presentation.

Final Answer:
PHP is an open-source server-side scripting language designed mainly for web development, used to generate dynamic content, interact with databases, and build full web applications on the server.