Inner Blocks are Gutenberg Blocks that allow inserting additional blocks within your own block. To understand it even better, imagine a shortcode that wraps the content. This content can then be shown or hidden. You can achieve that inside Gutenberg with Inner Blocks.
Gutenberg is coming and if your WordPress plugin is using shortcodes, you might consider building Gutenberg blocks out of the shortcodes. In this tutorial, we will not learn about converting shortcodes into Gutenberg blocks. We will learn how we can integrate Gutenberg blocks into your existing plugins.