copied from The Catholic Encyclopedia
Miracle Plays and Mysteries
These two names are used to designate the religious drama which developed among Christian nations at the end of the Middle Ages. It should be noted that the word "mystery" has often been applied to all Christian dramas prior to the sixteenth century, whereas it should be confined to those of the fifteenth century, which represent the great dramatic effort anterior to the Renaissance. Before this period dramatic pieces were called "plays" or "miracles". The embryonic representations, at first given in the interior of the churches, have been designated as liturgical dramas.
As for Calendar Girls, I have no idea - hence the 2 ?s !! ....except that they 'posed saucily' and the number of letters fitted.