NetBeans would be a development platform, or probably more commonly referred to as an IDE (Integrated Development Environment). As such, it is a software tool that helps you write, debug, and deploy your code. You can think of it essentially as a text editor on steroids.
A framework, on the other hand, is a set code which the developer then adds to in order to create an application, many of which currently implement some version of the Model, View, Controller (MVC) pattern. Popular examples in PHP would be CodeIgniter, CakePHP, and Zend Framework. You might want to check out these video tutorials to get a quick idea of how a framework can be used: http://codeigniter.com/tutorials/.