What's the difference between a green card and a permanent resident?

A green card is no different from a permanent resident.

The American permanent resident card, also known as the green card, is an identity document used to prove that foreigners have the status of permanent residents in the United States. "Getting a green card" refers to the immigration process of becoming a permanent resident. The legal permanent residency of green card holders is an official immigration benefit, including conditional permission to stay in the United States and get a job. The holder must maintain his permanent resident status, and if he no longer meets certain conditions required by the status, the holder may lose his status.