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Abstraction
An abstraction describes what something should do without actually showing you how to do it. According to the Microsoft documentation:
"An abstraction is a type that describes a contract but does not provide a full implementation of the contract."
Included as examples of abstractions are abstract classes and interfaces. Examples of abstractions in the .NET Framework include Stream, IEnumerable<T>, and Object. If the topic of abstraction seems a bit fuzzy now, don't worry. I will go into much more detail in the section on encapsulation and the difference between encapsulation and abstraction.