It's Bias and Variance
Recently my nephew got 97 marks in his mathematics test . I told the little kid , hey !! you have an accuracy of 97% to which he asked what does it means. I told him when you divide number of correctly answered questions by total number of questions you get the accuracy . Then I told him about error as well which basically means ratio of number of wrongly answered questions (assuming he answered every questions ) to total number of questions. Hope now you get the relationship between error and accuracy which is very much like higher the accuracy lesser the error and vice versa. Similarly in machine learning accuracy is the ratio of correctly classified data points to the total number of data points. Let's say in cat and dog classification , features of cat is given to model and if model classifies it as a cat then it is called as Correctly Classified point and if model classifies it as a dog then it is Misclassified point. Let's say we have total 1000 data points...