According the page on Amazon, this week's update makes one major change to the reading experience.
- Improved Tables Experience: Reading and navigating tables inside your books has been improved with optimized rows and column spacing, a pagination indicator to preserve context for multi-page tables, and a new pop-up table viewer with zoom and pan capabilities so you can interact with large tables at any font size.
Tables are a way of displaying content on webpages which website designers are not supposed to be using any more, but you still encounter them from time to time on websites (and in ebooks). And now the Kindle will make it easier to read them.
Amazon will be pushing the update out to all compatible devices, but you can also download the update and install it yourself. You'll find the update on Amazon.com.