Long exposure
Technique
A photo with a shutter speed of several seconds or more.
Makes waterfalls silky, clouds into sweeping streaks, car headlights into light trails. A tripod, remote shutter and ND filter during daylight are practically indispensable. Use Bulb mode for exposures longer than 30 seconds. Turn image stabilization OFF on a tripod - it can cause blur when there's no movement to compensate.
Tools that help with this: