What does it mean to expose the mobile phone for a long time?

Photography skills. Long exposure of mobile phone is a photography skill of opening the shutter for a long time. 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 can make the moving objects in the scene look charming and blurred. Common scenes are light rail and running water, which, like milk, have the feeling of fairyland.