The <figcaption> element
Short for ‘Figure Caption’. Contains a piece of content that gives a brief description of the main part of the <figure> element which is its parent.
Usage
This descriptive text (or other markup) is meant to allow the reader of the document to work out which figure the main text of the document is referring to. The caption might just be a description, or might be a reference number, or both.
The <figcaption> element is optional.
You don't need it at all if the figure can be identified easily on its own.
If it does appear, then it must be the first or last thing inside a <figure> element.
It's not allowed to appear anywhere else.
Whether you put a caption at the top or bottom of the figure doesn't affect its meaning, but being able to put it in either place makes it easier to decide how to lay out your document and style your figures with CSS.
Full list of attributes
All the usual HTML global attributes are available