-is the art or practice of designing and constructing buildings (Google Dictionary)
-the structure or design of anything (Dictionary.com)
-the art and science of designing and superintending the erection of buildings and similar structures (Dictionary.com)
-a style of building or structure (Dictionary.com)
-the style in which buildings are made (Cambridge Advanced Learner's Dictionary)
-the art and science of designing and making buildings to study architecture (Cambridge Advanced Learner's Dictionary)
My summary of Architectural Design:
Architectural Design is the designing of a structure, design or style of anything based on a principle of the needs/challenge.