I'm little confused why people are being so weird with the OP, asking what the difference between a blob and a file aren't something for seaweedfs lol, Blobs and Files, and other terms are terms used to describe different layers of data allocation in almost every modern object storage solution.
Blobs are what lie under files, you can have a file split into multiple blobs spread across different drives, or different servers etc, and then can put it back together into a file when requested, thats how i understand it at a basic level