I think it may actually be called the stone of Rosette. It's a chunk of basalt discovered in July 1799 in the small Egyptian village Rosette (Raschid), which is located in the western delta of the Nile. It is kept at the British Museum in London if you fancy a look. On it there are three inscriptions that represent a single text in three different variants of script,
The text appears in hieroglyphs (script of the official and religious texts), of Demotic (everyday Egyptian script), and in Greek. This allowed Jean Francois Champollion to decipher the hieroglyphs.