Runes are the letters of an alphabet called the runic alphabet. These letters were used in Scandinavian and German areas from about 2000 years ago until about a thousand years ago. They are still used as a kind of decoration on ornaments, sculptures and cards.
The Scandinavian runic alphabet is known as the futhark from their first six letters of the alphabet: F, U, TH, A, R, and K. The Anglo-Saxons also used a runic alphabet.
Runic letters belong to the pagan times before Christianity reached countries of Northern Europe. Soon afterwards, the runes were replaced by the Latin alphabet characters (the ones we use today).
The oldest runes are found in Denmark and northern Germany, suggesting that they were used here before Scandinavia. Runes are now popularly thought of as going with Vikings. As you will have learned, everyone used runes at the time.
The video below shows the Ruthwell Cross in Scotland. It is a Christian cross that was once in the open, but is now indoors. It has both Runic and 'English' characters on it, as you will see.