There are many definitions depending on discipline, but here is how I define it for strategic communications:
Building a visual language that connects a company’s vision and messaging to their marketing deliverables. This includes their brand, identity, web development and collateral materials. So often websites and print materials are designed without deep understanding of what an organization is and what it is wanting to become—the materials lack an authentic vision and end up looking “templated” (ie. this is what a “social activism” logo looks like, this is what a “medically related” NGO or foundation looks like, etc.) The design “strategy” is not there and even if a consumer can’t verbalize what is missing, they still recognize it is not as authentic as it could be.