The term 'The Piper' refers to a character in a German folktale, who is hired by the townspeople to rid their town of rats. The piper is paid for his services with a bag of gold coins, but when the townspeople refuse to PAY him, he uses his magical pipe to lure all the children away. The crossword solution for this term is PAY, which is an appropriate answer as it reflects the payment the piper was promised for his services.