According to Wikipedia's page on Architecture...
Architecture is...
The art and science of designing and erecting buildings and other physical structures.
The practice of an architect, where architecture means to offer or render professional services in connection with the design and construction of a building, or group of buildings and the space within the site surrounding the buildings, that have as their principal purpose human occupancy or use.
A general term to describe buildings and other structures.
A style and method of design and construction of buildings and other physical structures.
According to Wisegeek's page on "What is Architectural Design"...
Architecture is...
Architecture design refers to the actual design and layout of spaces. Architecture encompasses many different elements including construction, design, and the manipulation of light as it relates to shadow. Throughout history, architects have found ways to create functional and practical spaces using any materials that were available.
According to the Businessdictionary on "What is Architectural Design"...
Architecture is...
Concept that focuses on the components or elements of a structure or system and unifies them into a coherent and functional whole, according to a particular approach in achieving the objective under the given constraints or limitations.