A public-private partnership (PPP) is, broadly speaking, an arrangement between the public and private sectors, whereby some public sector services are provided by the private sector with clear agreement on the shared objectives for delivery of the public infrastructure or public services.
Such an arrangement usually requires the private sector party to design, finance, build or rehabilitate, operate, and maintain the infrastructure required to provide the public service.
Source: PPIAF: Overview of PPPs
Click here for a brief presentation on PPPs.
For more information on PPP arrangements, see the World Bank, PPIAF and IFC Infrastructure Resource Center on Laws, Contracts and Regulations.