1. What's PHP ?

The PHP Hypertext Preprocessor is a programming language that allows web developers to create dynamic content that interacts with databases. PHP is basically used for developing web based software applications.

2. What are the difference between abstract class and interface?

Abstract class: abstract classes are the class where one or more methods are abstract but not necessarily all method has to be abstract. Abstract methods are the methods, which are declare in its class but not define. The definition of those methods must be in its extending class.
Interface: Interfaces are one type of class where all the methods are abstract. That means all the methods only declared but not defined. All the methods must be define by its implemented class.

3. Explain the ternary conditional operator in PHP?

Expression preceding the ? is evaluated, if it’s true, then the expression preceding the : is executed, otherwise, the expression following : is executed.

4. What’s the difference between include and require?

It’s how they handle failures. If the file is not found by require(), it will cause a fatal error and halt the execution of the script. If the file is not found by include(), a warning will be issued, but execution will continue.

6. What is the difference between $message and $$message?

They are both variables. But $message is a variable with a fixed name. $$message is a variable who's name is stored in $message. For example, if $message contains "var", $$message is the same as $var.

7. Which one execute faster on php POST or GET?

Both are same while performing the action but using POST security is there.
Because using GET method in the action, form field values send along with URL, so at the time of sending password, problem will occur means password also will shown in the URL.
Using of POST there is no problem.

GET method has a limit of sending parameters 100 characters but POST method does not have a limit of sending data

GET is faster than POST. Because GET fetch the data directly from the URL but POST method fetch the encrypted data from the page.

8. What is the difference between ucfirst and ucwords?
ucfirst() to convert the first letter of every string to uppercase, and ucwords(), to convert the first letter of every word in the string to uppercase.

9. What Is a Session?

Sessions are commonly used to store temporary data to allow multiple PHP pages to offer a complete functional transaction for the same visitor.

10. What is the use of ob_start()?

Its intializing the object buffer, so that the whole page will be first parsed (instead of parsing in parts and thrown to browser gradually) and stored in output buffer so that after complete page is executed, it is thrown to the browser once at a time.