Bias and Variance

When trying to fit a machine learning model to a data, we would have faced scenarios where the model will work fine on the training data, but will fail miserably on the test data. In machine learning terms we will call that overfitting and it will be specified by using terms like bias and variance. Though most of us has got the understanding of what overfitting means, we still don't get the full picture of what is happening in the background. So, here I will give a clear picture of what is happening behind the scenes of bias and variance. First lets talk about target function, What is a target function?