PHP (Hypertext Preprocessor) is a server-side scripting language used to develop dynamic and interactive websites and web applications. It works seamlessly with MySQL and powers popular platforms like WordPress, Laravel, and many e-commerce websites.

• GET sends data through the URL and is mainly used for retrieving information.
• POST sends data in the request body, making it more secure for forms containing passwords or sensitive information.
• POST also supports larger amounts of data than GET.

• Session: Stores user information on the server and maintains user login until the session expires or the user logs out.
• Cookie: Stores small pieces of information in the user's browser and can remember user preferences or login details for future visits.

CRUD stands for:

• C – Create
• R – Read
• U – Update
• D – Delete

These are the four basic database operations performed using PHP and MySQL in most web applications.

PHP connects to MySQL using MySQLi or PDO. After creating a connection, SQL queries are executed to insert, retrieve, update, and delete records from the database.

OOP is a programming approach based on Classes and Objects. Important OOP concepts include:

• Class & Object
• Constructor
• Inheritance
• Polymorphism
• Encapsulation
• Abstraction

OOP makes applications more organized, reusable, and easier to maintain.

• include: Generates a warning if the file is missing, but the script continues execution.
• require: Generates a fatal error if the file is missing, and the script stops executing.

require is generally used for essential files like database connections and configuration files.

A secure PHP login system should include:

• Password hashing using password_hash()
• Password verification using password_verify()
• SQL Injection prevention using prepared statements
• Session management
• Input validation and sanitization
• CSRF protection for forms