Cavities and feathers are two common types of diamond inclusions. Typically, a cavity indicates a small hole in the diamond structure, but it can be entirely different in a VVS2 stone from that in an SI2 diamond. Moreover, the location of the cavity inclusion also affects their clarity grade.
Feathers, on the other hand, are small fractures within the diamond structure and are called so because of their feather-like appearance. Small feather inclusions that are well within the heart of the diamond will not be readily visible and are no reason for concern. Yet those that are visible to the naked eye can affect the value of the stone.
Minute cavities and feathers in a diamond usually do not affect the stone’s durability, so they are not “bad” inclusions. However, they do affect the clarity grading of the diamond and its visible quality, so they are important determining factors in the overall price of good diamond rings.