What is the difference between using "./" and not using it in file paths in PHP?

When specifying a file path in PHP, using "./" at the beginning indicates that the file path is relative to the current directory. If you do not use "./", PHP will look for the file path relative to the root directory of the server. It is important to use "./" when referencing files within the same directory or subdirectories to ensure the correct path is used.

// Using "./" in file path
include("./includes/header.php");

// Not using "./" in file path
include("includes/header.php");