What is the difference between using single quotes and double quotes in defining strings in PHP?

Using single quotes and double quotes to define strings in PHP can have different effects on how the string is processed. Double quotes allow for the inclusion of variables and special characters within the string, while single quotes treat everything as a literal string. If you need to include variables or special characters within the string, you should use double quotes. If you want to treat everything as a literal string, single quotes should be used.

$name = "John";
echo "Hello, $name"; // Output: Hello, John

$name = "John";
echo 'Hello, $name'; // Output: Hello, $name