What is exponential accuracy? How many types of accuracy are there?

Question

I am reading and working on some function approximation methods. I did not quite understand "Exponential Accuracy" which is mentioned in multiple works in literature. I searched the internet only to find the mentions about it but not a definition about it. There are other types of accuracies like linear, logarithmic and quadratic... It sounds something simple or isn't it that simple? A good reference will help and thanks for the help.