The “file object” discussed is part of the vector store. It is the file ID element that you can attach “attributes” metadata to, for example.
Vector store files represent files inside a vector store.
It is also what is billed when it is in a vector store. Files that are simply in the files endpoint in your storage are not billed.
There is no mechanism to auto-delete files themselves. They may additionally be attached and employed by multiple vector stores.