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.

There are 3 kinds of attributes that you can add to your HTML tags: Element-specific, global, and event handler content attributes.

The <dfn> element accepts the following attributes.

Element-Specific Attributes

This table shows the attributes that are specific to the <dfn> tag/element.

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 HTML5 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 Handler Content Attributes

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.

Below are the standard HTML5 event handler content attributes.

Again, you can use any of these with the <dfn> element, as well as any other HTML5 element.

For a full explanation of these attributes, see HTML 5 event handler content attributes.

Differences Between HTML 4 & HTML 5


To see more detail on the two versions see HTML5 <dfn> Tag and HTML4 <dfn> Tag. Also check out the links to the official specifications below.


Here's a template for the <dfn> tag with all available attributes for the tag (based on HTML5). These are grouped into attribute types, each type separated by a space. In many cases, you will probably only need one or two (if any) attributes. Simply remove the attributes you don't need.

Note that the <dfn> element does not actually have any local attributes (i.e. attributes that are specific to the element), but the following global attributes and event handlers are available to the element (and all other HTML elements).

For more information on attributes for this tag, see HTML5 <dfn> Tag and HTML4 <dfn> Tag.

* The title attribute has special semantics on the <dfn> element. If used, then the exact value of the attribute is the term being defined.

Tag Details

For more details about the <dfn> tag, see HTML5 <dfn> Tag and HTML4 <dfn> Tag.


Here are the official specifications for the <dfn> element.

What's the Difference?

W3C creates "snapshot" specifications that don't change once defined. So the HTML5 specification won't change once it becomes an official recommendation. WHATWG on the other hand, develops a "living standard" that is updated on a regular basis. In general, you will probably find that the HTML living standard will be more closely aligned to the current W3C draft than to the HTML5 specification.