Singly quoted strings are treated almost literally, whereas doubly quoted strings replace variables with their values

A string is a data type used to represent text. It is a set of characters

Variable scope is known as its boundary within which it can be visible or accessed from

There is no need to write a dollar sign ($) before a constant, where as in

To define a constant you have to use define() function and to retrieve the value of a constant,

Built-in datatypes in PHP: Integer - whole numbers String - alphanumeric text Float - decimal point numbers(also called double)