[buffaloseven]

Widows define how many lines of a paragraph must be visible on the top of a page:

The widows property sets or returns the minimum number of lines for an element that must be visible at the top of a page (for printing or print preview).

Orphans define how many lines of a paragraph must be visible on the bottom of a page:

The orphans property sets or returns the minimum number of lines for an element that must be visible at the bottom of a page (for printing or print preview).

Kobo's default settings for widows and orphans are (in many people's opinions) too high, and it can result in entire paragraphs being shifted to the next page instead of breaking them more naturally. This can result in large amounts of white-space on a page instead of the page being full of text. If you want to correct that, you just need to create a file in the root (the main directory) of your Kobo e-reader called kobo_extra.css. Open that file up with a text editor (such as notepad if you're running Windows) and paste the following code into it:

body {
    widows: 0;
    orphans: 0;
}

...then save the file. In Calibre, open the preferences and click on Plugins and then open the preferences for the KoboTouchExtended driver and make sure Modify CSS is checked, then hit OK.

I ejected my e-reader then plugged it back in and let Calibre re-recognize it just to make sure everything was up to date.

A secondary advantage to re-uploading all your books with the 2.1.0 version of the KoboTouchExtended driver is that there have been fundamental changes to how it modifies your ePub files. Starting with this version, annotation features -- in particular highlights -- should work much more reliably on your kobo-ified ePubs. All the ePubs I've tested highlights on so far have worked wonderfully. You don't need to do any extra work for this (i.e. you need to do none of the steps I described above), just re-send your books.

Hope this helps explain it a bit!