In the PMI PMBOK guide, Risk is defined as always in the future and is an uncertain event or condition that, if it occurs, has an effect on at least one project objective (usually in the area of budget, schedule or quality).
Risk is the scourge of project management as it is the only ‘unplanned’ event that the project team must try to first, identify, and secondly, determine the effect of this uncertainty on the overall project or organizational goals then thirdly, attempt a strategy to minimize the impact. Risk is managed throughout the project life cycle and each risk is placed into the project Risk Register. (See below example of Risk Register)