The article gives a detailed and vivid overview of various results related to defect describing the role it plays in local uniformization and the structure theory of valued fields. Several interesting examples of finite extensions with non trivial defect are given. A method to classify Artin-Schreier defect extensions is also described. The generalized stability theorem, the independence theorem regarding defect and the theorem on henselian rationality are stated along with a list of open problems.
For the entire collection see [Zbl 1201.13001].