What does long exposure of photography mean?

Exposure with a shutter time slower than 1 sec can be called long exposure.

Long exposure is an exposure mode with slow shutter (long exposure time). The advantage is that you can shoot dim scenery more clearly, and you can also shoot fantastic pictures, such as waterfalls and city roads at night. Long exposure photography needs to use a long shutter speed to capture the image blur of fixed elements, while moving or blurring ugly elements.

Long exposure photography is a kind of photography technology that opens the shutter for a long time. It is often used for night photography, ray photography and waterscape photography.

Extended data:

Long exposure photos are usually taken in bulb mode rather than at standard shutter speed. B mode allows us to freely choose exposure lasting more than 60 seconds. Another healthy practice when using long exposure is to turn on the ISO noise reduction setting, because even at low ISO sensitivity, the amount of aurora reaching the sensor may cause noise in the final image.

This is due to a phenomenon called "hot pixels", in which some pixels of the camera sensor do become very hot and generate noise. When our image is enlarged to 100%, this noise is considered as a red/green/blue pixel in our image.

Baidu encyclopedia-long exposure photography