An indulgence is defined as "the remission before God of the temporal punishment due for sins already forgiven as far as their guilt is concerned." Indulgences may be partial or plenary. A partial indulgence removes part of the punishment; a plenary indulgence removes all of it. The punishment may be in this life, or in the next life, in purgatory.
Indulgences were sold by the Church until 1567. They continued to be granted without financial transaction until they fell out of favour in the 1960s. However it appears they have recently been reinstated.