This is an interesting question. Lets look at couple of definitions starting with Wikipedia’s definition
“Enterprise architecture (EA) is "a well-defined practice for conducting enterprise analysis, design, planning, and implementation, using a holistic approach at all times, for the successful development and execution of strategy. Enterprise architecture applies architecture principles and practices to guide organizations through the business, information, process, and technology changes necessary to execute their strategies. These practices utilize the various aspects of an enterprise to identify, motivate, and achieve these changes.”
The Wikipedia definition is actually a quote from Federation of EA Professional Organizations, Common Perspectives on Enterprise Architecture, Architecture and Governance Magazine, Issue 9-4, November 2013 (2013).
ISO/IEC 42010:2007 defines "architecture" as:
"The fundamental organization of a system, embodied in its components, their relationships to each other and the environment, and the principles governing its design and evolution."
TOGAF has two definitions for Enterprise Architecture that incorporates the ISO definition the:
1. A formal description of a system, or a detailed plan of the system at component level to guide its implementation
2. The structure of components, their inter-relationships, and the principles and guidelines governing their design and evolution over time
I like to think of Enterprise Architecture as way of aligning technology to business goals and principals. Analogies to traditional architecture approaches are often used when discussing enterprise architecture. One that I have heard quoted many times is the example you wouldn’t build a house room by room with no idea about how you wanted to the final house to look upon completion. It would end up out control with a very haphazard look and feel to it.
Enterprise architecture is intended to provide you with a design, a view, a model of what your technology and application infrastructure will look like that is designed to meet the purpose of your organisation.
It important to remember that traditional architecture looks at building physical things. Enterprise Architecture looks at building virtual things. Both provide a view of how the thing or object will look like after the building/development work has been completed.