Everyone has their own 'most important bits' of what OOP is. For example, many people don't consider message passing to be an important part of OOP, others do.

Everyone has their own 'most important bits' of what OOP is. For example, many people don't consider message passing to be an important part of OOP, others do. Like any term that corresponds to an idea rather than a thing, each person is going to have their own take on what that idea is based on their experiences.