A Caption is text that usually accompanies a figure or table in a book.
A caption is used to identify the content of the figure or table and optionally it may include a unique identifier that can be used to reference a figure or table in the book text. In cases where there are many figures or tables there may be a TOC specifically aimed at listing those items for easy reference. In an eBook these lists are generally clickable to jump directly to the item. There are usually identified as LOF, List of Figures, or LOT, List of Tables, respectively.
 Figure Caption
A Figure Caption is text usually just below or just above the image itself. For more see Figure#Captions.
 Table Caption
Sometimes a Table caption or table title is inside the table itself on the first line but usually it is text outside the table but inside the table tag, either just below it or just above it. Caption is a defined tag for ePub but it is not honored in some eBook readers to maintain the same page.
 Potential Problems
Captions in eBooks that can flow such as ePub are often problematic since it can be difficult to ensure that the caption is shown on the same page as the figure or table. CSS can sometimes be used to control this using 'avoid-break' but some eBook readers do not honor the CSS settings.
 Potential Fixes
One way to fix this on some eBooks is to force a page change just prior to the figure or table there by ensuring that there is sufficient room for a page in the book. Another way is to use SVG format to encapsulate your image (even if the image itself is bitmapped). SVG can allocate a larger canvas with room for the caption.
A crude way that will always work for images is to simply place the caption on the image itself using an image editor. A margin can be added to the picture for the caption. This technique will not allow the caption to be searched for.