As I have previously said almost everything in content server is an asset. Specifically they are an instance of type asset. In FatWire a page is an asset, so is an image, an address or a name.
An asset has metadata & attributes, there are some standard ones such as name or createddate. You can also define your own attributes if you wish, such as contributor or colour etc.
Due to the manner in which FatWire is set up you can also have assets as attributes of another asset. In the case of a page asset you may have added an image (blob) and another page, in this case the image and the other embedded page are both attributes of the first asset.
FatWire Lesson 2: What is an Asset
