Christmas Cheer was a form of energy and a fuel source in various Multiverses where Christmas was celebrated on Earth. Its uses varied from reality to reality, ranging from bringing happiness to people to powering Santa Claus' sleigh after it had crashed in New York.
Little is known about the nature of Christmas Cheer, though through careful observation, it has been determined that Humans cause Christmas Cheer by being positive and having happy thoughts and feelings around the Christmas holidays. According to Buddy the Elf, "The best way to spread Christmas Cheer is to sing it loud for all to hear."
How said advice could be applied to an individual who does not know the meaning of Christmas Cheer is unknown, but the fact remains that Christmas Cheer is a very potent power source, and effort has been made in an attempt to tap it.