base

n. a support on which something is applied or built; a carrier; a substrate an alkali

Notes

For paper documents, paper is the base that supports the ink, graphite, or other material that forms the words or images of the content. Photographs may use paper, transparent or opaque plastic, ceramic, glass, metal, cloth, or other materials as a base to support the light-sensitive chemicals that form the image. Magnetic media used for audio or digital recordings often use a polyester base.