I have seen several definitions of digital transformation floating are twitter of late. I thought I would document mine here:

Digital transformation is the manifestation of strategy enabled by digital technology. 

Business models, policies and practices, branding, the use of space and the adoption of technology should all be driven by strategy. It should be noted that digital transformation is a bit of a red herring, because digital transformation, while an apt goal, is not a strategy, but simply one way to implement strategy. Strategy is not a goal, but directive action, and as such, it is the foundation of organizational transformation.