ok so my kid went out and left her doll head unattended so I thought I'd provide a little illustration. Yes, it's quick and nasty but I hope it helps.
First off we've got the light going straight on at the subject, as you can see this is your basic passport photo type shot - it's flat as a pancake.
Moving along, with the same single light I positioned it at 45° to the subject to case some shadow and give it some depth and is what's known as Rembrandt lighting or what I think the classical artist types mean by Chiaroscuro.
Finally I put the light at 90° to the subject to create the distinct shadow as per the OP. This is split-lighting. [-]Yes, there was a little light creeping in the shadow side - I could have reshot it properly or darkened the shadow completely in post but you get the idea. Besides, I've got to shoot some soccer later and didn't want to dedicate too much time on this rather than chilling out.

[/-] (Ok, I fixed it in post)