Wikipedia defines it as: Social Innovation refers to new strategies, concepts, ideas and organizations that meet social needs of all kinds - from working conditions and education to community development and health - and that extend and strengthen civil society. Over the years, the term has developed several overlapping meanings. It can be used to refer to social processes of innovation, such as open source methods. Alternatively it can be used to describe innovations which have a social purpose - like microcredit or distance learning.
The concept can also be related to social entrepreneurship (entrepreneurship isn't always or even usually innovative, but it can be a means of innovation) and it also overlaps with innovation in public policy and governance.
Social innovation can take place within government, within companies, or within the nonprofit sector (also known as the third sector), but is increasingly seen to happen most effectively in the space between the three sectors.