What does the "Class 'Illuminate\Foundation\Application' not found" error typically signify in a PHP application?

This error specifically indicates that the PHP interpreter cannot locate the `Application` class, which is a core component of the Laravel framework. It's usually a `Fatal Error` because Laravel applications heavily rely on this class to bootstrap the entire framework. The error almost always points to an issue with Composer dependencies not being installed or the autoloader not being correctly generated, preventing PHP from knowing where to find the `Illuminate\Foundation\Application` namespace and its corresponding file.