MOBI

A specific and closed format from Amazon for Kindle readers. It can only do the flow variant. Limited support for text formatting and control over images (as a book creator). Its successor is AZW3. From Miguel's point of view, there is nothing to do with it, just convert it from another format (EPUB) and send it to the customer.

Miguel converts to MOBI format using Calibre, which makes e-books look much better than using the official KindleGen tool.