Archival medium
From The Glossary of Digital Photography
Material designed to hold a digital image without deterioration, permanently. The material must be stored and handled under archival conditions, with special regard for light, temperature, humidity, and air quality. In reality, there is no material that meets this strict standard. Therefore archival medium is not a strict technical term. Instead, it is used in a casual sense to reflect a material's relatively long life compared with other types of materials. Accelerated testing is usually conducted to ensure the longevity of photographic and computer materials.
