The <mark> element is new in HTML5 and is used to mark or highlight text in a document "due to its relevance in another context".¹ (opens new window)

The most common example would be in the results of a search were the user has entered a search query and results are shown highlighting the desired query.

<p>Here is some content from an article that contains the <mark>searched query</mark>
that we are looking for. Highlighting the text will make it easier for the user to 
find what they are looking for.</p>

Output:

(opens new window)

A common standard formatting is black text on a yellow background, but this can be changed with CSS.

Bold Text

To bold text, use the <strong> or <b> tags:

<strong>Bold Text Here</strong>

or

<b>Bold Text Here</b>

What’s the difference? Semantics. <strong> is used to indicate that the text is fundamentally or semantically important to the surrounding text, while <b> indicates no such importance and simply represents text that should be bolded.

If you were to use <b> a text-to-speech program would not say the word(s) any differently than any of the other words around it - you are simply drawing attention to them without adding any additional importance. By using <strong>, though, the same program would want to speak those word(s) with a different tone of voice to convey that the text is important in some way.

Italic Text

To italicize text, use the <em> or <i> tags:

<em>Italicized Text Here</em>

or

<i>Italicized Text Here</i>

What’s the difference? Semantics. <em> is used to indicate that the text should have extra emphasis that should be stressed, while <i> simply represents text which should be set off from the normal text around it.

For example, if you wanted to stress the action inside a sentence, one might do so by emphasizing it in italics via <em>: "Would you just submit the edit already?"

But if you were identifying a book or newspaper that you would normally italicize stylistically, you would simply use <i>: "I was forced to read Romeo and Juliet in high school.

Underlined Text

While the <u> element itself was deprecated in HTMl 4, it was reintroduced with alternate semantic meaning in HTML 5 - to represent an unarticulated, non-textual annotation. You might use such a rendering to indicate misspelled text on the page, or for a Chinese proper name mark.

<p>This paragraph contains some <u>mispelled</u> text.</p>

To mark some expression as an abbreviation, use <abbr> tag:

<p>I like to write <abbr title="Hypertext Markup Language">HTML</abbr>!</p>

If present, the title attribute is used to present the full description of such abbreviation.

To mark text as inserted, use the <ins> tag:

<ins>New Text</ins>

To mark text as deleted, use the <del> tag:

<del>Deleted Text</del>

To strike through text, use the <s> tag:

<s>Struck-through text here</s>

To offset text either upward or downward you can use the tags <sup> and <sub>.

To create superscript:

<sup>superscript here</sup>

To create subscript:

<sub>subscript here</sub>

Syntax

• <abbr>Abbreviation</abbr>
• <b>Bold Text</b>
• <del>Deleted Text</del>
• <em>Emphasized Text</em>
• <i>Italic Text</i>
• <ins>Inserted Text</ins>
• <mark>Marked (or Highlighted) Text</mark>
• <s>Stricken Text</s>
• <strong>Strong Text</strong>
• <sub>Subscript Text</sub>
• <sup>Superscript Text</sup>
• <u>Underlined Text</u>