This question probably should have been #1 on my list of Top Enterprise Architect Questions, but I’ve given it number 4. The answer is lengthy, and I usually take at least an hour in my Architect Bootcamp classes to explain this one in detail. I get into great depth as to the various roles in IT Architecture, the relationship from one to another, as well as the relationship between the architects and the stakeholders, project managers, developers and other technologists.
In a nutshell, the role is to facilitate the creation of alternatives or solutions to a business problem where a combination of technologies and processes may be the solution. The EA role is to facilitate appropriate research, discussion and synthesize the alternatives and compare them to the appetite for risk and a match to the business strategy direction.
Here is a video that I shot that gives some context and describes some of the skills required for the role, and a couple of high level points in understanding the role.