A Christmas song is a song which is normally sung during the Christmas period, and usually has some Christmas or winter related theme. If the song is traditional, or specifically has a religious content, then it is often called a Christmas carol, though some might also be called Christmas hymns.
Some songs, such as White Christmas, are songs which have become popular over the Christmas period, and often songs are introduced in films, specifically for Christmas. Such songs are not strictly Christmas carols.
Examples of Christmas songs include:
"The Christmas Song" (also known as "Chestnuts Roasting on an Open Fire") was written by Mel Torme.