Mark up the defining instance of a term:
The <dfn> tag represents the defining instance of a term in HTML.
The defining instance is often the first use of a term in a document.
The nearest parent of the <dfn> tag must also contain the definition/explanation for the term inside <dfn>.
The term inside the <dfn> tag can be any of the following:
1. The content of the <dfn> element (without a title attribute):
2. The title attribute of the <dfn> tag:
3. The title attribute of an <abbr> tag inside the <dfn> element:
You can also add an id attribute to the <dfn> element. Then, whenever a term is used, it can refer back to the definition using an <a> tag:
The <dfn> tag also supports the Global Attributes in HTML.
The <dfn> tag also supports the Event Attributes in HTML.
HTML tutorial: HTML Quotation Elements
HTML DOM reference: DFN Object
Most browsers will display the <dfn> element with the following default values: