Data Science is

fundamentally an interdisciplinary subject. It comprises three distinct and overlapping areas: the skills of a statistician who knows how to model and summarize datasets (which are growing ever larger); the skills of a computer scientist who can design and use algorithms to efficiently store, process, and visualize this data; and the domain expertise – what we might think of as “classical training” in a subject – necessary both to formulate the right questions and to put their answers in context.

Drew Conway’s Data Science Venn Diagram illustrates this: