Public-Private Partnerships (or P3s) involve a partnership between a government agency and a private-sector company with a common goal in mind.
P3s are often used to share risk and resources between the two parties. Common examples of P3 relationships are operations contracts for public parks - the government agency such as the U.S. Forest Service may own and manage the asset, but a private-sector company may be responsible for operations and maintenance of the park. These types of relationships often benefit both parties - the government agency can lower their operations costs and the private-sector company can use their efficiencies to win a new long term client.