From Appropedia

Backcasting refers to the activity of making decisions or policies based from starting in the future, a future in which one envisions that the objectives are being realised. The practitioner, policymaker, analyst, etc., works back from this endpoint to work out the policy measures that are needed to achieve this endpoint, including the timescales needed. The feasibility of environmental, social and economic impacts are assessed against the endpoint's realisation.

Backcasting is an ongoing process that is open to different possible futures worthy of exploration. It is a visualisation tool, not a final or ready-made solution, a guide to achieving a most desirable future.

It is a way of making space for policies, programs and norms that are not yet coherent, feasible or even acceptable but that could be given a series of gradual steps taken towards that endpoint.