Predictability describes the likelihood at which an event is going to occur. When a person predicts something they are guessing what will happen in the future based on past results and events. When something is predictable it means that it is likely to occur because it happened in the past.
Predictability can be qualitative (such as predictable behaviors) or quantitative (such as the statistical prediction of results based on data). The predictability of an organism's behavior can be high or low.
An example of high predictability would be a mouse who was trained to push a lever after it sees a light. It receives food after it pushes the lever. After the mouse has been trained and repeated this task hundreds of times there will be a high predictability that the mouse will hit the lever once it sees the light again.