Object Oriented Programming (OOP) is a programming structure that is based on the concept of classes and objects. In object-oriented programming the focus is on the creations of objects which contain both data and functions together.

Below is a quick overview of PHP 5's key features:

PHP 5 Quick Overview:

1. Object-Oriented Programming (OOP) Support

• In PHP 5 you manage objects in code easier way.
• You could now organize your code better using classes and objects.
• Control Access to object properties and methods like public, private, and protected.

2. Improved MySQLi Extension:

• In PHP 5 MySQLi (MySQL Improved) extension was introduced for improved interaction with MySQL databases.
• It had more features and better security compared to the older method.

3. Exception Handling:

PHP 5 introduced a way to deal with errors more effectively called "exception handling."

4. SimpleXML:

The SimpleXML extension was added for easy manipulation of XML data.

5. SOAP Extension:

PHP 5 made it easier to communicate with other web services using the SOAP extension

6. Namespace Support

7. Better Performance:

PHP 5 ran faster compared to PHP 4, meaning your websites and applications could load quicker.

8. Magic Methods:

Magic methods, such as __construct, __destruct, __get, and __set, were introduced to handle certain operations automatically.

9. Improved Error Handling:

Enhanced error handling mechanisms with the introduction of the error_reporting function.

10. Zend Engine 2:

PHP 5 featured the Zend Engine 2, providing performance improvements and a more modular architecture.

11. Security Improvements:

PHP 5 included various security enhancements, making it more resilient against common security vulnerabilities.

12. CLI (Command Line Interface) Support:

PHP 5 allowed running PHP scripts directly from the command line, without needing a web server.

13. SQLite Support:

PHP 5 included built-in support for SQLite, a lightweight database system.