The Phaistos Disc was found in the Minoan Palace of Phaistos (Φαιστού) on Crete in 1908 by Luigi Pernier, an Italian archaeologist. It is thought to date from the 2nd millenium BC: the middle or late Minoan Bronze Age. On it are inscribed 242 symbols, 45 of which are unique, which spiral from the outside the the centre of the disc.
The symbols, which appear on both sides of the disc, are pictographic representations of every day things, such as people, birds, plants and tools. The symbols are grouped on the disc with lines between each group, and they have been given numbers and names by scholars such as Arthur Evans.
Many attempts have been made to decipher the symbols on the disc, however none have been successful. Some believe the script to be a syllabary, others an alphabet, and others a logographic script. No other examples of this script have been found, so unless that happens, it is unlikely that the script will be deciphered.
Another possibility, which Peter Aleff discusses in his book, Solomon's Sky, is that the symbols are not writing at all, and that the disc is a kind of board game with symbols representing constellations of stars.
Here are the the unique symbols that appear on the Phaistos Disc in order of frequency, with the names given to them by scholars.