An Environmental Management System (EMS) is, simply put, a set of recognized standards using principals of quality control to identify and manage environmental aspects of an organization. At its core is the establishment of systems of continuous improvement that seek to identify and address the institution's environmental impacts. 
ISO 14000 is a specific type of EMS that uses internationally established standard elements of allow for a common expectation. These common aspects allow an EMS to be audited and verified which allows external observers to understand that at a very basic level an organization is observing their environmental impact.
ISO 14000, nor any other EMS, has goals and commitments that are required. The performance based nature of the EMS, and other system based measures, is that it applies specifically to an individual institution. Therefore they do not have to waste time verifying pieces that are not relevant to their operation. This is the opposite of most mandates and regulatory requirements which establish a base threshold without any consideration of the operation. This leaves one institution to pursue goals that may not be the same as another similar institution, but allows for the corporate culture to partially influence which impacts are addressed. This will often lead to better internalization of the goals compared to those forced by an external agency. 
One primary characteristic to address is the fact that an EMS, even an ISO 14000 certified system, does NOT protect the environment from environmental impacts, but instead establishes a quality framework that ultimately requires action for completion.