Simplifying the description of a read-world entity to its essentials. A named, tangible representation of the attributes and behavior relevant to modeling a given entity for some particular purpose. Don't endow the abstraction with powers and ability beyond the actual entity. The specification of the interface should be independent of the implementation. A single interface can have multiple implementations.
Several interfaces can share implementations.
Only the whole is visible and accessible. A collection of interacting parts that are externally visible.