Profiles are groups of settings used to filter books based on certain properties.
Quality
Quality profiles filter books by their extension. You can select different extensions like MOBI, EPUB or PDF to download. In these profiles they can also be ordered by preference and de-selected to ignore that format. You can also allow upgrades so if a format you prefer becomes available, it will be downloaded.
Metadata
Metadata profiles filter books based on their metadata (author, language, isbn, rating, series, etc).
Delay
Delay profiles are used to specify a delay (in minutes) before downloading a book. It also allows you to set the priority between torrent and usenet.
Release
Release profiles allow you to set specific terms to look for (or ignore) when grabbing releases.