Design patterns·Objects, messages and the principles
two parents both define the method and the language has to pick one, and which one is a rule you had to look up.
Diamond problem
Also calleddeadly diamond, multiple inheritance ambiguity
The ambiguity when a class inherits the same member along two different paths from a shared ancestor. It is the standard reason a language bans multiple inheritance of implementation and offers interfaces or mixins with an explicit resolution order instead. Knowing the term matters mostly for reading a linearisation error message and for the interview question about why one language allows it and another does not.