A library feature is a frequently used feature, or combination of features, that you create once and then save in a library for future use. Most feature types are supported, some with certain limitations.
Library features usually consist of features added to a base feature, but not the base feature itself. Because you cannot have two base features in a single part, you cannot insert a library feature that includes a base feature into a part that already has a base feature. However, you can create a library feature that includes the base feature and insert it in an empty part.
You can create commonly used features, such as holes or slots, and save them as library features. You can use several library features as building blocks to construct a single part. This can save time, and it can help ensure consistency in your models.