a photography technique in which the exposure is made up of parts lit at different times. In practice:
  1. Choose a dark scene. Dark like a moonlit night, or the inside a room at daytime with closed curtains and no artificial lighting. Your light meter should be reading more or less off scale, or some absurdly long time.
  2. Mount your camera on a tripod, or set it on something absolutely solid.
  3. dial a long exposure, such as 30 seconds. Even better, if your camera has it, use the B or T setting, in order to have the shutter open for an arbitrarily long time.
  4. set the lens at f4. You will probably have to estimate focus.
  5. open the shutter
  6. light up the parts of the scene you are interested in using various lights such has hand-hald flashlights, portable strobe lights, deer lights. Use color filters for additional effects. Use multiple strobe shots for large, distant subjects. Read up on flash guide number to estimate strobe exposure.
  7. repeat and bracket.

One good starting point for this technique is to place "accents" of light on parts of a naturally lit scene. For example, you can have a moonlit field and light up some specific trees or a group of people or a car, or a rockface. You are going to have all sorts of color shifts, so you should not really expect highly realistic pictures.

If you are into digital photography, you can take repeated exposures of the same scene you can later mount them using Photoshop. This will take much of the guesswork out of the taking phase.

A photographer's site where the techinique is used, one could say even a bit too much: http://www.deanchamberlain.com/

thanks to Grzcyrgba and to SharQ