1. A person - usually a saint - depicted as carrying his or her own head. For a saint, the depiction often refers to martyrdom by beheading.
2. (medical) a cephalostat designed to take in-sequence-oriented facial photographs and gnathostatic models. (I think that definition refers to a head-stabilizing mechanism and camera usually used to take dental photos.)
Etymology: Greek, "head carrier", from kephale, head, and pherein, to carry.
Saint Denis, patron saint of Paris, was said to have walked six miles with his head in his hands, while preaching a sermon.
Although the word is traditionally used in reference to saints, it can refer to any head-carrier;
non-saint cephalophores include the Headless Horseman, and the Green Knight from Arthurian legends.
Chhinnamasta, "she whose head is severed", is a self-decapitated goddess recognized by both Hindus and Buddhists. She is often depicted with (among other things) her own severed head drinking one of the jets of blood that spurts from her neck.
On a lighter note, They Might be Giants wrote a song about cephalophores:
"The way you swing your head while strolling fancy free,
Or melting down some army guys to make green tea,
Though there are millions of cephalophores
That wander through this world,
You've got something extra going on...."