From the toxel.com design blog:

Light writing is a form of stop motion animation wherein still images captured using the technique known as light painting are put in sequence thereby creating the optical illusion of movement for the viewer.

Two examples:

Impacto Criativo (Creative Impact)

Created by Propague and MidiaEffects with 2 cameras, 1700 clicks, 18 people, 20 nights, 35 flash lights, and 234 batteries.

…and:

Light Paint Piano Player

Created by Ryan Cashman with a small green LED keychain light. The frames were photographed with a Canon Rebel using 20-30 second exposure time.

See them all. (Warning: visiting the toxel.com home page can be hazardous to one’s productivity.)