# What is the prediction accuracy?

In simple words, what is the prediction accuracy? What is it based on? How does it help? When is it used?

For example, suppose that you observe the sequence of numbers $$1, 1, 2, 3$$. What would be a likely next number of this sequence? The operation of guessing this number is called a prediction. These are numbers of a Fibonacci sequence, so a model could predict $$5$$ as the next number of this sequence. However, it could also predict e.g. $$2$$ because the complete sequence could be $$1, 1, 2, 3, 2, 1, 1$$. Which prediction is correct? It depends on the problem. Do we want the model to predict the numbers of the Fibonacci sequence or of another sequence? Suppose that we want the model to learn the Fibonacci sequence and the models predicts another number different than $$5$$, then this will be considered an incorrect prediction.