A widget is an interactive object you can add to your book. iBooks Author provides the following widgets:
Gallery: A sequence of images your readers can navigate through, each with its own custom caption.
Media: A movie or audio file readers can play.
Review: A sequence of interactive multiple-choice or drag-to-target questions.
Keynote: A slideshow or other presentation created with Keynote.
Interactive image: A graphic with callouts (labels); readers can view detailed information about specific parts of the graphic.
3D: A COLLADA (.dae) file readers can manipulate.
Scrolling Sidebar: Content (with text, images, and shapes) that’s related to the surrounding text but isn’t part of the main text flow. In the completed book, readers can scroll through the contents of the sidebar separately from the rest of the page.
Popover: An overlay (with text, images, and shapes) that opens when the reader taps or clicks an image in the completed book.
HTML: An HTML5 widget (with the extension .wdgt).
Note: Not all the widgets are available in EPUB templates.