After having spent nearly 20 years writing 'Enterprise' software here is my answer :
1) Enterprise almost always means 'web application'.
2) Enterprise really just means 'very very large'.
Enterprise software is typically written by hundreds of people over several years. Thus the tools, patterns, and languages used tend to make collaboration, security, stability and scaleability a priority.
The typical 'Stack' of an enterprise application will involve many different languages, protocols, servers, firewalls.. each with their own teams of people.
These applications require many different skill sets to produce, from project management, through to actual software engineers.
Often people working on any particular aspect of an enterprise scale application don't know exactly how their component fits. Only the "Enterprise Architect" may see the whole picture, but then they don't know any of the details.
The art of enterprise application creation is successfully navigating this 'fog of war' by choosing the right technologies and procedures etc.