Means 10. Dix is a philosophy created by Mana, leader of Moi Dix Mois. It represents "1" meaning his start of something new, and "0" which represents his vision as a universal artist. Thus, "Dix" which translates literally to 10 in french, is essentially a philosophy, hence "Moi Dix Mois" (me ten months) which has an important meaning to Mana Sama and all Dixtors of the world.
"Dix love!" Said the Dixtor of Dixanadu. XD