HTML <dfn> Tag

The HTML <dfn> tag represents the defining instance of a term.

The defining instance is the instance where the term is being described or defined. This is typically when the term is being used for the first time. There is no need to use the <dfn> each time you refer to the term. You only need to use it at the point that the term is being defined.


The <dfn> tag is written as <dfn></dfn> with the term inserted between the start and end tags.

Like this:


Basic tag usage

Using the <dfn> Tag with Abbreviations

Abbreviations enclosed in the <abbr> tag can include the abbreviation's expansion in the title element. However, this expansion is not the defining instance. The <abbr> tag can contain the expansion every time it appears in a document, but the defining instance (i.e. using the <dfn> tag) should only appear once.

The following example demonstrates this. Note that the abbreviation and expansion appears twice, however the defining instance (i.e. using the <dfn> tag) only appears once.


Attributes can be added to an HTML element to provide more information about how the element should appear or behave.

The <dfn> element accepts the following attributes.

None, but the title attribute has special semantics for this element. If the <dfn> tag has a title attribute, then the exact value of that attribute is the term being defined.

Global Attributes

The following attributes are standard across all HTML elements. Therefore, you can use these attributes with the <dfn> tag , as well as with all other HTML tags.

For a full explanation of these attributes, see HTML 5 global attributes.

Event Handlers

Event handler content attributes enable you to invoke a script from within your HTML. The script is invoked when a certain "event" occurs. Each event handler content attribute deals with a different event.

Most event handler content attributes can be used on all HTML elements, but some event handlers have specific rules around when they can be used and which elements they are applicable to.

For more detail, see HTML event handler content attributes.