Definition:
Co-design is a well-established approach to creative practice, it has its roots in the participatory design techniques developed in Scandinavia in the 1970s. Co-design is used as an umbrella term for participatory, co-creation and open design processes. This approach enables a wide range of people to make a creative contribution in the formulation and solution of a problem.
This approach goes beyond consultation by building and deepening equal collaboration between affected users attempting to, resolve a particular challenge. A key tenet of co-design is that users, as ‘experts’ of their own experience become central to design process. The immediate benefits of applying co-design approach includes generation of better ideas with a high degree of originality and user value, improved knowledge of customer or user needs, immediate validation of ideas and concepts, higher quality, better differentiated products or services, more efficient decision making, lower development costs and reduced development time, better cooperation between different people or organisations and across disciplines.
Further Reading:
Book: Hardware/Software Co-Design: Principles and Practice By Jorgen Staunstrup, Wayne Wolf
https://en.wikipedia.org/wiki/Participatory_design#Co-design
http://designforeurope.eu/what-co-design
https://medium.com/@thestratosgroup/co-design-a-powerful-force-for-creativity-and-collaboration-bed1e0f13d46