Wikipedia states that architecture is 'the art and science of designing and erecting buildings and other physical structures'. So architectural design means designing and erecting buildings and other physical structures. (from http://en.wikipedia.org/wiki/Architecture)
Answers.com says architecture is 'buildings and other large structures', so architectural design is designing buildings and other large structures. (from http://www.answers.com/topic/architecture)
The MacBook dictionary's definition of architecture is 'building', which means that architectural design is designing buildings.
Also architectural design can be time, period, culture and location specific.