Social innovation is a term used globally to describe and identify quite different activities. While it is a term that everyone likes to use, precisely what it refers to is not always clear. This paper from three students of the first course of the Master of Arts of Social Innovation explores different definitional approaches or intentions –legitimating, theoretical, action-reflection, broad and distinctive– and considers why a definition of social innovation is important and what the crucial ingredients, informed more by practice than theory, might be. Following lessons learnt from postmodernity and critical theory, social marketing, democracy, governance and social entrepreneurship, we arrive at a definition that is value-laden, distinctive and focused -from inception to impact -on equality, justice and empowerment.