Bulb Ramping, or "Bramping", as it is commonly called, is a technique of creating time-lapse videos by using the 'bulb' mode of the camera, and controlling each exposure using an external timer. These type of time-lapse videos tend to give very smooth transition between day and night (and vice-versa), instead of the flicker you tend to get if you leave the exposure for the camera to determine (or if you change the exposure manually).
Compare the video above (created using the 'Bramping' technique), to the one below, in which the exposure was manually increased to compensate for the rapidly changing light. The changes in exposure give the video (the one below) a very jarring effect. In fact, this was my first attempt at time-lapse during a sunset.