What is a Hazard? 

A hazard is anything that may cause you as a driver or rider to change speed or direction. Broadly speaking hazards can be broken down into three categories;

Static hazards are features on the road that do not change. Examples would be bends, road junctions, roundabouts, pedestrian crossings. When approaching these you may have to change speed and/or direction. You may also have to take into account the action of other road users, such as at a junction.
Moving hazards can generally be classed as other road users. These include car drivers, motorcyclists, cyclists, pedestrians, bus/lorry drivers, horses and other animals. You will need to be aware of each of these road users for differing reasons; cyclists may swerve to avoid objects on the road such as drain covers, bus and lorry drivers need more room to manoeuvre, horses and other animals may be easily startled, etc.
Environmental hazards include the weather and lighting conditions. Some examples are; A bright setting sun in the autumn can affect your visibility Rain will increase your stopping distance Snow or ice will increase your stopping distance by at least ten times Night time can make it difficult to see other road users (particularly cyclists and pedestrians) and to judge the speed and position of other road users.