A Christmas carol sextet is a group of six singers who perform Christmas carols. The term 'sextet' comes from the Latin word for six, and it is used to describe any ensemble of six musicians or singers. In this particular crossword, the solution for the term 'Christmas carol sextet' is 'GEESE, ' which refers to the traditional Christmas carol 'The Twelve Days of Christmas, ' which features six GEESE a-laying.